We could, and should, do a lot more in recovering tax from corporations that trade in the UK yet use accounting techniques to place profits elsewhere.
For which there is an ongoing Global initiative with many major economies/countries working together to try to find ways to improve transparency in Global firms towards getting them to pay taxes in the countries they trade from in a fairer way. There's growing demand from many countries for fairer taxes to be paid, but you need global agreement to make changes to laws. Tax haven countries (such as Isle of Man, Gibraltar, BVI, Panama) rely on the tax avoidance industry so aren't particularly keen on co-operating and thus losing a great chunk of their revenue/economy!
HMRC are also working hard to tackle the most blatant abuses. There has been recent court cases, such as against Google who tried to argue that their UK staff weren't actually "selling" anything but were just support staff, whereas HMRC produced plenty of evidence that UK staff were indeed heavily involved in direct selling to UK customers. Trouble is that the big global firms have larger numbers of expert in house staff and larger resources than HMRC, so it's not a level playing field and HMRC can't tackle everyone at once and these court cases take years from start to finish, so it's very long term.
Such a shame that previous heads of HMRC did "sweetheart" deals with the likes of Vodafone whilst under Blair/Brown's watch.
At the end of the day, the "global" economy facilitated by the WWW has left most governments languishing behind in all kinds of ways, not just re taxation, and they're having to play catch up because they didn't react quick enough at the beginning.