If you're not going to need the money for that sort of period of time then you should at least consider equities - either direct share investments (more tax advantageous due to CGT treatment) or indirect share investments (e.g. a low charges unit linked investment fund - but less tax advantageous due to the exit tax/8 year deemed disposal treatment, but also arguably simpler than holding shares directly).
You should have a read of some of the many existing general investment threads to get some more info and ideas.