A share is worth what people are willing to pay. So you have sold one for £1. If you sell another share for £1000 to someone else then the price per share/company valuation at that point is £1000 (per share issued) so you would have made the frist share worth this as well....
On paper of course. And no one would pay it unless they genuinely thought that your company would either give adequate return in the form of dividends or a much higher sales/exit price at a time in the future.
The though to ponder though, if you can grow your company 1000% in a year, and need only £1 investment - why do you let this other person invest? Seems a raw deal for you the entrepreneur. I would just have put in the £1 myself.
To previous poster - no you don't have to be a plc, a private limited company can sell shares too. If you need guidance on business funding then How to fund your buiness by Steve Parks is an excellent read. You can get it on Amazon here:
http://www.amazon.co.uk/How-Fund-You...7673059&sr=8-1
Good luck with your business growth
