I wouldnt invest 4000£ in a single cash isa as suggested here.
I went to lloyds recently and they said that the maximum amount of saving has increased so you can save 5100£ every tax year as opposed to the last year 3200£ (maximum) every tax year. Anyway the interest you get are still not much. About 2.8% gross. I wouldnt advise you to a cash isa if you want to invest in a good saving account. The cash isa is for minimum risk investors.
Halifax 3 years ago was offering a massive 4.75% interest at (3 years) deposit.
I think now this gross has gone down if you go to halifax and ask for a leaflet, they will provide you with all the savings account available.
There is some other saving which takes into account a fixed rate of 3.5 % in the first year and then euribor 6months for the next 3/4 year at HSBC.
The best option is really send your money to an Indian trusted bank and control your money abroad. If you have a good amount of money such as 50k you wouldnt have to work anymore. Would be enough to live in India at a massive rates of 8%. With the indian cost of life, you would have a life of a king.
Take other things in consideration when you invest in a term deposit, such as the need for money in the short time. Question related to marriage, purchase of an asset, mortgage, etc etc.