I'm planning Bramley 20 as a targeted race next year. Something nice about racing a 20 rather than training for a marathon and having to run a 20 as a "not quite full out but hard enough to knacker you" effort.
OO53, Fulham Palace parkrun is a good fast one, as is Dulwich. There is one in Greenwich itself but I understand it is not the fastest.
10 miles before lunch (12:00 noon meeting) so I was under a tight deadline to get it done, first 5 at 7:21 pace then the next 5 at 7:09 pace for 7:15 average.
Gul, people are built differently so, as OO53 says, some will be better at the shorter stuff and some at the longer stuff. You have a lot of what it needs to deliver a 3.0x marathon but if your body just isn't tuned that way then treat marathons as something to enjoy and concentrate on racing shorter stuff for the glory.