Simple, Bombproof and Fixed

£800 is a lot of money, I would consider buying something complete, totally blinging and secondhand off ebay or here. Or just buy a nice frameset and sling some decent parts on it. Depends how bombproof you want it to be? 36 hole wheels, alu or cromo cranks, tricks / polo or flat out. other framesets to throw into the mix are FBM's, BJ's, Bricklanes Own brand frames.

Careful, none of those are particularly strong frame sets, at least not on the same level as volume cutters and charge plugs anyway.
If I had £800 I'd spend out on strong basic components, cheap out on the unimportant stuff like saddles cranks and pedals, and then upgrade those as and when they break.
Thats pretty much what I did, and I put a lot of stress on my bike, I would go with:

A cutter or plug frame

MTB forks, with a low axle to crown height (around 410-430mm works pretty well on 700c wheels)
A bmx stem and some strong as fuck riser bars such as gusset open prisons (which have 22.2mm diameter tubing for bmx stems) will give you a bomb proof front end

Goldtec/Phil Wood hubs on some touring rims (Rigida and Mavic are the best way to go here) either 36H or 48H depending on how mental you're planning on going with your bike

A minimum of 28-32c tyres (your rim choice will also dictate minimum tyre width to a degree) if you want good protection for your wheels, I find 32c to be a good compromise between speed/shock absorption, sure its not as fast as skiny tyres, but I can throw my bike around without killing my wrists and its still reasonably fast albeit requiring a little more effort to get up to speed!

All this will give you a really good solid base from which to build from, which will be strong enough for tricks/polo/whatever you want to throw at it, and as long as you get yourself a decent bottom bracket you replace your cranks later as and when you need to, probably worth starting off with something cheap such as Sugino Messengers if you're on a budget. As my bike is becoming more and more tricks specific i'm probably going to go up in tyre size at the front to a 40c at least, but all these little adjustments can be made later on down the line once you decide what you will be doing with your bike the majority of the time, hope that all helps a bit.