The highest interest invariably comes with the highest risk. If you do not understand the risks, you should avoid overseas accounts and investing in shares. It would be worth splitting the sum between a couple of savings accounts as the UK bank guarantee covers the first £35k if the bank fails. I am sure that if you put the word round your neighbourhood that you are looking to invest £70k, you will get lots of suggestions but you should only deal with people/organisations that you trust.
In the long term, the best investment might be investing in where you live by moving to a nicer property. Capital gains on your main residence are not currently taxed and you get to enjoy the investment by living there.