//Maybe if the REALLY big tax dodgers were made to pay up (Google, Facebook, City traders, Quark, etcetera), //
it's important to note that what these companies are doing represents avoidance, not evasion, and it's currently perfectly legal. the government announced tax on royalties relating to uk sales last year, but it's not due to be applied until the start of the next fiscal year.
if there's a belief that a punitive regime needs to be applied to multinational companies then vote for the party the promises to do just that. but be careful what you wish for - companies will continue to look to protect their profits and if that means legging it somewhere with a less stringent tax regime that's what they'll do, and they'll take their tax dollars and people's jobs with them.