Unfortunately I think the Post Office (is that National Savings & Investments?) has just withdrawn the index-linked savings certificates again because of the high demand.
If you're worried about fees on investments, investment trusts tend to be cheaper than unit trusts - they don't have initial charges and the annual fees tend to be lower. 8 years is just about long enough to consider equity investment, though if you're relying on it for uni fees or whatever, you might need to move out of shares gradually over the last couple of years to avoid a big market sell-off hitting the value just when you need the money back.
Don't forget Junior ISA is just around the corner, and will allow you to save up to £3,600 a year into cash and/or stocks and shares (you can have one of each type of account but the £3,600 applies across both) that is locked in until DD is 18.
Or there are childern's savings plans like the Children's Investment Plan from F&C or the Jump Savings Plan from Witan that don't have the tax breaks of JISA but also don't have the lock-ins, and can either be held in trust (again, DD's proeprty but no access until 18) or as a 'designated' account, which remains your property.
The latter is taxed as yours and the former as hers.
You might need to be a bit careful with how you set your investments up to avoid the £100 rule. (This states that money given by the parent is taxed as if it were the parent's if it produces income in excess of £100pa). As it's your DD's inheritance it's obviously not technically coming from you, but if you are opening the accounts you may find you need to make this clear. (Disclaimer: I've never actually tried to do this myself so am not quite sure how it works!)
Good luck.