Unfortunately the fact you live in a flat and consequently traverse two flights of stairs daily (however achieved) is I would think, likely to mitigate against any successful claim for DLA. Based on the GP's assessment of the likelihood of worsening of condition, and that lack of space means you're unable to store a scooter which might make short journeys alone viable, it would seem that living in flat is going to become increasingly unsustainable. Sounds like it's time to seriously weigh up the pros and cons of relocating to somewhere else until retirement. Possibly moving farther out of Chelmsford, but remaining on the main line, where house prices will be that bit lower?

http://www.nationalrail.co.uk/passenger_services/disabled_passengers/wheelchairs_scooters.html