What is the best way to invest £30K for under 1 year

Hi carolem36, and welcome to the forum.

Assuming you've used your cash ISA allowance for the current tax year, then you could consider a 6 month fixed rate bond (there aren't many of these around) or an instant access account.

Have a look here compare fixed rate bonds, instant access accounts, and cash ISAs...

http://www.money.co.uk/savings-accounts.htm

Possibly, if you know when you want it back, a deposit with a notice period, e.g. if the notice period is 90 days just make sure you ask for the withdrawal (closure) 3 months before you want it. Time consuming to research all the T&Cs tho' I will admit.