I've seen them doing such counting before, but I've never seen them close an entrance/exit for it. Just what on earth could they hope to achieve by doing this? The only possible explanation I can think of is that they were short of staff, and instead of postponing or simply counting one side one day and the other side the next day, they decided to inconvenience thousands of commuters instead.

Incidentally, you can find details of station usage at http://www.rail-reg.gov.uk/server/show/nav.1529

Here are stats for London (inner and outer) stations for total entries and exits 2005/06, with Forest Hill and Honor Oak Park highlighted in bold and red.

WATERLOO LONDON 61,036,093
VICTORIA LONDON 47,859,728
LIVERPOOL STREET LON 47,271,234
LONDON BRIDGE 37,416,180
CHARING CROSS LONDON 28,562,268
EUSTON LONDON PART O 27,166,829
PADDINGTON LONDON 26,501,166
KING'S CROSS LONDON 20,301,663
CANNON STREET LONDON 17,613,560
FENCHURCH STREET LON 15,746,318
EAST CROYDON 15,398,123
CLAPHAM JUNCTION LON 12,426,542
WIMBLEDON 11,800,551
KINGS CROSS THAMESLI 8,820,810
BLACKFRIARS LONDON 8,258,915
STRATFORD 7,699,178
VAUXHALL LONDON 7,686,894
RICHMOND 7,348,300
MOORGATE 7,263,068
MARYLEBONE LONDON 6,819,287
EALING BROADWAY 5,996,873
SURBITON 5,772,843
FINSBURY PARK LONDON 5,041,828
BARKING 4,908,499
WATERLOO (EAST) STAT 4,904,157
ST PANCRAS LONDON 4,893,313
ROMFORD 4,823,860
SUTTON (SURREY) 4,749,567
CITY THAMESLINK 4,644,522
BROMLEY SOUTH 4,474,726
PUTNEY 4,261,221
LEWISHAM 4,021,074
ORPINGTON 3,716,456
UPMINSTER 3,331,240
WALTHAMSTOW CENTRAL 3,294,336
BALHAM 3,236,366
KINGSTON SURREY 3,226,866
QUEEN'S PARK (GREATE 3,147,282
TWICKENHAM 3,139,142
EARLSFIELD 2,756,054
ILFORD 2,623,618
SIDCUP 2,395,111
NEW CROSS GATE LONDO 2,352,894
LIMEHOUSE 2,312,496
RAYNES PARK 2,287,130
BEXLEYHEATH 2,259,630
WOOLWICH ARSENAL 2,091,677
ABBEY WOOD 2,089,975
ELEPHANT & CASTLE 2,056,783
NEW CROSS 2,041,661
HITHER GREEN 2,029,848
FOREST HILL 2,006,798
BLACKHEATH 2,005,382
WILLESDEN JUNCTION 1,976,305
FELTHAM 1,966,655
STREATHAM COMMON 1,897,201
PURLEY 1,891,142
BECKENHAM JUNCTION 1,864,281
NEW MALDEN 1,840,780
NORWOOD JUNCTION 1,829,363
DENMARK HILL LONDON 1,817,818
THORNTON HEATH 1,816,383
ELSTREE 1,815,251
HAROLD WOOD 1,773,086
NEW ELTHAM 1,742,900
ELTHAM 1,731,197
GREENWICH 1,701,826
GIDEA PARK 1,670,663
WELLING 1,660,007
PETTS WOOD 1,619,168
HERNE HILL 1,618,701
NORBURY 1,590,579
PECKHAM RYE 1,580,382
CHADWELL HEATH 1,556,568
SYDENHAM 1,544,882
HARROW & WEALDSTONE 1,516,874
GROVE PARK 1,478,280
TEDDINGTON 1,469,222
WORCESTER PARK 1,453,302
KEW GARDENS 1,354,836
WALLINGTON 1,286,304
STREATHAM HILL 1,274,689
BROCKLEY 1,256,952
KENSINGTON OLYMPIA 1,244,273
HAYES & HARLINGTON 1,238,789
NORBITON 1,211,152
GUNNERSBURY 1,204,250
ENFIELD TOWN 1,191,561
BARNEHURST 1,176,408
STREATHAM 1,143,780
GIPSY HILL 1,133,747
SEVEN KINGS 1,095,940
HIGHAMS PARK 1,091,726
MORTLAKE 1,087,936
LEE 1,086,477
GOODMAYES 1,070,419
ST MARY CRAY 1,050,117
COULSDON SOUTH 1,039,995
CRYSTAL PALACE 1,038,211
WEMBLEY CENTRAL 1,037,956
CRAYFORD 1,028,431
HONOR OAK PARK 1,023,807
CHINGFORD 994,515
SHORTLANDS 983,508
BATTERSEA PARK LONDO 973,657
MILL HILL BROADWAY 972,856
EDMONTON GREEN 925,507
MOTTINGHAM 916,667
FOREST GATE 915,549
CHARLTON 908,725
ELMSTEAD WOODS 889,503
BEXLEY 888,178
TULSE HILL 886,932
KENSAL GREEN 881,370
HACKNEY DOWNS 868,010
CLOCK HOUSE 867,552
SOUTHALL 859,286
BARNES 848,648
WANDSWORTH TOWN 845,840
CHISLEHURST 836,871
HAMPTON COURT 828,675
HAYES (KENT) 825,633
WANDSWORTH COMMON LO 822,024
DALSTON KINGSLAND 821,558
CATFORD 816,133
WEST DRAYTON 799,977
CARSHALTON 798,202
PALMERS GREEN 794,683
WEST NORWOOD 794,560
CATFORD BRIDGE 788,198
WHITTON 786,410
SOUTH CROYDON 772,355
ALBANY PARK 764,994
PLUMSTEAD LONDON 763,273
SELHURST 763,111
ST MARGARETS (GREATE 762,648
FALCONWOOD 758,999
STONELEIGH 758,146
WINCHMORE HILL 749,965
RAINHAM (GREATER LON 741,429
EAST DULWICH 725,479
WEST WICKHAM 717,374
NEW BECKENHAM 714,340
CHEAM 705,233
ALEXANDRA PALACE 692,845
ENFIELD CHASE 689,469
CAMDEN ROAD LONDON 688,609
WEST HAMPSTEAD 680,256
NEW BARNET 674,532
MANOR PARK 656,895
SANDERSTEAD 652,771
WEST CROYDON 651,164
GORDON HILL 650,873
HAMPTON 648,359
TOOTING 645,316
LADYWELL 644,466
ELMERS END 643,131
KIDBROOKE 641,786
CHELSFIELD 626,644
OAKLEIGH PARK 623,602
PENGE EAST 596,134
WEST HAMPSTEAD THAME 594,263
WEST DULWICH 583,287
BICKLEY 581,455
MOTSPUR PARK 575,097
ENFIELD LOCK 569,880
MAZE HILL 564,557
HACKBRIDGE 549,637
STRAWBERRY HILL 543,620
WESTCOMBE PARK 528,172
HOUNSLOW 516,873
BRENTFORD 514,596
HACKNEY CENTRAL 513,943
CARSHALTON BEECHES 504,983
KENT HOUSE 495,618
BELLINGHAM 484,386
NORTH DULWICH 479,909
BUSH HILL PARK 479,449
STONEBRIDGE PARK 473,765
BROMLEY NORTH 471,533
THAMES DITTON 464,935
BELVEDERE 451,835
ERITH 447,065
HAMPTON WICK 445,580
BETHNAL GREEN 445,506
KENTISH TOWN LONDON 443,644
CRICKLEWOOD 432,477
NUNHEAD 425,168
ACTON CENTRAL 416,037
BRIXTON 412,621
WEST BROMPTON 411,667
HENDON 403,528
PURLEY OAKS 401,317
GOSPEL OAK 397,700
LONDON AIRPORT TCKT/ 395,673
HAMPSTEAD HEATH 388,289
QUEEN'S ROAD PECKHAM 386,716
HORNSEY 381,659
KENLEY 374,987
EDEN PARK 374,186
WEST EALING 371,096
HARLESDEN 368,147
DEPTFORD 361,345
HOMERTON 359,920
CROFTON PARK 339,599
WOOD STREET 339,194
HATCH END 337,687
ST JAMES STREET 333,283
CLAPTON 329,235
KENTON 321,286
HARRINGAY 317,815
LOUGHBOROUGH JUNCTIO 317,371
BRIMSDOWN 315,148
NORTH WEMBLEY 313,734
WADDON 311,613
SYDENHAM HILL 306,100
CHISWICK 304,367
ISLEWORTH 302,887
NEW SOUTHGATE 299,461
LOWER SYDENHAM 291,888
BRONDESBURY 287,849
TURKEY STREET 286,281
CHESSINGTON NORTH 285,980
KEW BRIDGE 271,445
PENGE WEST 270,751
WOODMANSTERNE 269,473
SLADE GREEN 269,130
MALDEN MANOR 268,334
SOUTHBURY 263,038
SYON LANE 263,012
ST JOHNS 261,374
WHITE HART LANE 259,945
TOLWORTH 251,745
FULWELL 246,114
SOUTH BERMONDSEY 245,667
HADLEY WOOD 244,961
SUNDRIDGE PARK 242,480
ANERLEY 235,382
QUEENSTOWN ROAD(BATT 234,932
RIDDLESDOWN 221,374
BOWES PARK 213,675
SILVER STREET 213,286
WOOLWICH DOCKYARD 212,245
NORTH SHEEN 211,199
CHESSINGTON SOUTH 206,316
STOKE NEWINGTON 203,512
KENSAL RISE 200,527
GRANGE PARK 197,636
MARYLAND 196,927
FINCHLEY ROAD & FROG 196,379
KENTISH TOWN WEST 190,998
SOUTH KENTON 185,022
REEDHAM (GREATER LON 184,430
SMITHAM 177,913
MITCHAM JUNCTION 175,089
BERRYLANDS 174,464
RECTORY ROAD 171,522
CANONBURY 164,672
KNOCKHOLT 157,505
HAYDONS ROAD 157,468
BRUCE GROVE 152,833
BECKENHAM HILL_TICKE 152,015
HANWELL 148,018
BARNES BRIDGE 143,772
CALEDONIAN ROAD & BA 135,634
RAVENSBOURNE_TICKET 126,221
BRONDESBURY PARK 125,507
PONDERS END 121,529
NORTH WOOLWICH 118,920
DRAYTON PARK 118,426
ESSEX ROAD 115,680
WEST SUTTON 104,981
CLAPHAM HIGH STREET 101,912
STAMFORD HILL 101,296
SUTTON COMMON 97,481
HEADSTONE LANE 95,077
DAGENHAM DOCK 91,936
WEST RUISLIP 91,527
ACTON MAIN LINE 87,880
NORTHOLT PARK 84,617
SOUTH ACTON 80,995
HACKNEY WICK 79,617
WEMBLEY STADIUM 78,049
WIMBLEDON CHASE 74,491
WANDSWORTH ROAD LOND 66,787
NORTHUMBERLAND PARK 66,370
CUSTOM HOUSE LONDON 66,184
KILBURN HIGH ROAD 59,041
BELMONT SURREY 57,688
CANNING TOWN 57,475
LONDON FIELDS 55,632
ST HELIER 53,088
SOUTH MERTON 50,424
UPPER HOLLOWAY 47,992
SOUTH HAMPSTEAD 46,146
CROUCH HILL 44,680
CAMBRIDGE HEATH 43,024
SOUTH TOTTENHAM 42,090
HARRINGAY GREEN LANE 34,025
CREWS HILL 33,372
LEYTON MIDLAND ROAD 32,407
EMERSON PARK 31,523
WALTHAMSTOW QUEENS R 30,503
MORDEN SOUTH 27,263
LEYTONSTONE HIGH ROA 26,724
WANSTEAD PARK 25,757
WOODGRANGE PARK 25,256
SILVERTOWN&LONDON CI 24,765
BLACKHORSE ROAD 22,593
BIRKBECK 21,642
CASTLE BAR PARK 19,893
ANGEL ROAD 15,786
SUDBURY HILL 10,210
SOUTH GREENFORD 6,106
DRAYTON GREEN 5,254
SUDBURY & HARROW ROA 2,538
HEATHROW EXP 4 178

Forest Hill was 52nd and Honor Oak Park 102nd out of 317 London stations.