If you take out a policy for 25 years and you survive the 25 years, you do not get any money back. You were paying premiums to cover the risk of dying. If you don't die within that term, the money you paid in premiums goes toward paying for the claims of all the other customers who did die. And if you did die, the money that your family got would be paid by the customers who lived.
The point of term insurance is that in case you die, your family members will be able to pay for expenses/pay back loans, mortgage, etc. You are paying for the peace of mind that no matter what happens to you, your family will be OK financially.
If you want, you can take out another policy after the 25 years, but it would be much more expensive considering how old you would be, and you might not need it at that time (e.g. mortgage is paid off, children are grown and independent).
Here is an explanation from the FSA:
http://www.moneymadeclear.fsa.gov.uk/products_explained/life_insurance.htmlForgot to add that I think most companies require you to be a UK resident, but not a citizen, but you would have to check with the individual company. You would have to check their terms and conditions to see if they would pay if you died outside the UK, but I can't see why they wouldn't, as long as you fulfilled all the other conditions.
