Both, to some extent, with that extent depending on (1) where opportunities arise where those immediately concerned have an interest in it happening, and (2) how much additional housing is needed to get prices down to something more sensible - the 'elasticity of demand'. On (1), I would expect most opportunities which arise to be extending or dividing up their houses - and please note the omission of your suggestion of extending any mortgages. I have a case in point in mind, of some neighbours - you may well know them - I'll pm the name - who continue to live in their family home, but some years ago converted the ground floor to a granny flat, and now have it rented out to some tenants. I doubt if any mortgage was needed here, since these are people of the baby boomer generation, who have lucked out so much in the post war era. This seems to me entirely wholesome, allowing people to age while maintaining their links with the local community, and not 'block bedrooms'. However, in the NOTES OF PLANNING POLICY WORKSHOP HELD AT DEPTFORD LOUNGE – 25th April 2012, where there were several representatives of amenity societies, although maybe not from FH Soc - we read only of opposition to conversions.

Extensions are more problematic, but still something I would welcome on balance. The plus points are as with conversions, and with the additional benefit of physically adding more habitable rooms per hectare, rather than just getting those that exist better used. The downside is the impact on neighbours if done badly, and the environmental impact of loss of garden space if the extensions are horizontal rather than vertical - which they will be unless there is planning guidance in place, because it will be so much cheaper. I'd prefer to leave the issue of loss of gardens for another discussion, since it's rather muddied by sanctimoniousness of the 'grow your own' type.

To be continued - I didn't realise there was a limit on the length of essays allowed on sse23.com