how can I make £800 in 8 days..?

In all seriousness:

1. Get an extension on paying,
   
2. Extend your credit - personal or business,
   
3. Sell some things - especially any random crap you don't need anyway, then
   
4. Look for quick ways to make money.
   
   
   

I'm guessing you've exhausted your contacts on the electrical work side? Tried every friend relative or connection. Then call up every building co you can think of.

Then try some of the random ideas here.