There's really no point leaving it where it is - you're getting no interest on it, which means the real value of the lump sum is actually going down.
What you should or could do depends on when or if you need the money, and how much risk you're prepared to accept. If you expect significant further rate rises, you could consider putting it into a short term fixed rate bond (three or six months) while you wait for interest rate hikes. On those you should get about 3.5%.
To maximise your interest on a very low risk approach, you could put it on deposit with Rabo or Northern Rock (over 4%.. check out savings and investment, or financial best buys forum), and maybe drip-feed into a high interest regular saver account - AIB's is giving about 7% on new regular savings, though this is for a limited period. If rates go up - as expected - you could then transfer your lump sum into a higher-interest fixed rate account.
If you're prepared to take more risk, and take a longer term approach, you could buy into tracker funds - but note that there is a risk to your capital with almost all of these, and you have to be prepared to leave your money in for longer.
There's no one right answer, but letting it sit in your current account is of no benefit at all... except to the bank!
