Something else to take into account with travel insurance is where you're travelling to. This is more true for annual worldwide policies. as once you've bought the insurance you don't need to inform the insurer of where and when you're going on future trips.
For example, I have an annual worldwide policy with Boots (underwritten by Chartis Insurance UK Ltd). However, it does not provide cover to (or through) Cuba, Afghanistan, Sudan and Liberia. While the last three are unlikely to be an issue for most holiday makers, Cuba is obviously a very popular destination and I'm sure many insurers don't exclude it. So it's always worth checking the small print for destination exclusions too.
Further to this, and I suspect common to most insurers, is that you will not be covered for travel to a country or area where the FCO has advised against all but essential travel before your trip. As this is constantly changing it's worth checking this as it can effect popular destinations (one current example is Thailand). There are also many tour operators offering tours in less well known and more adventurous destinations some of which may be on the FCO's lists. They are likely to have experienced staff in situ keeping an eye on things so your safety will not be compromised - but your insurance cover may be.
Check the FCO advice here:
http://www.fco.gov.uk/en/travel-and-living-abroad/travel-advice-by-country?action=essentialTravelParts#essentialTravelParts