why sell up when your making a good living?
for what you would get for it wouldnt be worth after all your hard work building it all up!
Don't do it mate!
hes won the lottery

I won it as well a couple of weeks ago but the £10 won't change my life

Seriously though - about the business. It really is a tough call on that. I mean, what would the vans and equipment be worth between them £6 - £20k depending on age and condition? Also, the premises? I assume that isn't part of the sale unless you have bought it outright. Then there's the work. £5k a month and very well established. Assuming good hourly rates can be earned that could be worth a fair premium. However, 2.5k turnover per man/van per month although OK, isn't anything particularly special but the work is well established and someone could start work the same day they bought it and could build on it or cherry pick the work. Are there any written/signed contracts with the commercial work? Would you agree not to trade (as a window cleaner) in the area for a certain period? Or are you cherry picking the best bits to simplify your life a bit? (nothing wrong with this IMO so long as you don't seek your old customers).
I'm not asking this with a view to buying I hasten to add but these are things that would need to be discussed and agreeed to when calculating a price.
Work often sells for 2 - 4 times monthly turnover. I unserdtand that there is a bubble in your area and it sometimes goes for 10x. If 10x + mid range equipment price, plus an agreement not to trade for several years, a shot in the dark tells me around £55k - £60k. However, if the work is not top work and you want to continue trading (without encroaching) maybe £30 - £35k. It really is a tough one to call though. A top quality round with top quality equipment/newish vans maybe as high as 80k even - though I reckon this would be top whack. You may even be better off to split it in two as it's possible you could get a bit more for each half.
As ever, it's only worth what someone is prepared to pay and if you would be prepared to take that.