It depends.

If you just need to buy insurance for a special travel, you could find the best offer using google because the offers are different at different time. If you travel a lot and stay less than 31 days out of uk, a lot of bank accounts have this kind of benefit ( for example, Natwest advantage gold, however, you need to pay monthly fee, of course other benefits are also available for this card), if you travel several times this year, you can try annual insurance from Barclays.