Because under the terms of its government bailout, RBS has the right to sell new shares to the government at 50p per share, or roughly twice the currentprice(in technical terms, 50p is the conversion price of RBS's 'B' shares).
Since uranium is 20 times cheaper to find than oil, (in terms of finding cost's share of sale price), the currentprice run-up has already spawned hundreds of exploration companies, where there were only a handful a decade ago.