Well we've drifted off house prices...

The main reasons Dacres Wood and Garthorne Road Nature reserves are not open to the public is that they are nature reserves rather than human habitats. Both sites back onto the railway line and Dacres Wood contains a pond. These aspects of the sites mean that they are potentially dangerous. Furthermore when Dacres Wood was open, it was used as a dump by some people and this can be a disaster for any natural habitat.

Dacres Wood is now open at least once a month but relies on volunteers to manage access. Devonshire Road is open at least twice a month in the summer but is a larger site and has more volunteers. Garthorne Road Nature Reserve is rarely open to the public and as far as I'm aware has no volunteers to do anything.

If you do want to visit a nature reserve, any time of year, there is the Horniman Nature Reserve at the bottom of the park, with a pond at the end which is carefully fenced off. Even better is Sydenham Woods which is a massive area of woodland for Inner London and great at this time of year if you like mud!