You should always have travel insurance when you go overseas. But you should also make sure that you're covered for all the things you want to do while you're away.

And there are some things that can invalidate your cover wherever you are.

Gocompare has highlighted 10 things that could lead to a travel insurance claim being rejected.

1: Not declaring pre-existing conditions

When an insurer works out your premium, they are essentially calculating how likely you are to make a claim. If you have a pre-existing condition, whether that’s something physical like angina or epilepsy, or some form of mental or nervous disorder, then you must declare it at the outset.

Yes, this will make your policy more expensive, but failing to declare it could mean your cover is useless anyway.

2: Preventable or avoidable medical treatment/conditions

If you fail to take prescribed medication, or you travel against medical advice, then your insurance is at risk. This also includes not getting the recommended inoculations for the country you are visiting.

[Related story: How to pay less for travel insurance and money]

3: Excessive alcohol consumption

This one is fairly self-explanatory. If you have got hopelessly drunk and hurt yourself as a result, your insurer probably won’t pay out for your claim.

4: Sports and adventurous activities you're not covered for

A standard travel insurance policy won’t cover you for certain sports, such as skiing, bungee jumping, quad biking, rugby, paragliding or martial arts.

If you’re likely to be getting up to something ‘adventurous’ on your trip, make sure your policy specifies that you are covered in case it all goes horribly wrong!

5: Not taking reasonable precautions

Insurers will expect you to take reasonable precautions to avoid injury, illness, disease, loss, theft or damage. In other words, don’t take liberties.

6: Reckless or illegal behaviour

Another fairly self-explanatory one this. If you are reckless, whether that’s sitting on a balcony railing or jumping off a wall, then you will likely struggle to make a claim if you end up hurting yourself.

Some insurers also rule out any claim from unauthorised use of a swimming pool outside the specified opening times.

7: Going to volatile destinations

If you head somewhere that the Foreign & Commonwealth Office (FCO) or the World Health Organisation has advised you to avoid, then your cover is at risk.

Countries that the FCO currently says Brits should avoid include Syria, South Sudan, the occupied Palestinian territories and Lebanon.

8: Travel paid for using loyalty schemes or points

Some policies exclude claims for unused travel or accommodation that was arranged using things like air miles, loyalty points or timeshares.

9: Not arranging visas and other documents

Make sure you arrange visas or any other official documentation for the countries you plan to visit. Fail to do so and your insurance may be invalidated.

10: Working without suitable cover

If you want to work while you’re abroad, whether that’s voluntary charity work or you are on a business trip, then you must make sure your policy specifically covers these activities.