For more information and things to bear in mind when choosing a policy, see below:
A European Health Insurance Card (EHIC ) gives residents of EU and EFTA countries the right to medical treatment in the rest of the EU and EFTA on the same basis as residents of those countries. It costs nothing to obtain a card (in the UK, at least) and can be obtained very easily and quickly by applying online. You must take the card with you to be able to use it. They do expire, so check yours is still valid when you start to plan your trip.
Although it is well worth obtaining an EHIC if you are eligible for one, or finding out about other reciprocal health agreements if you are not an EU/EFTA resident, this should not be viewed as a substitute for travel insurance. Schemes like EHIC will not provide any help if, Heaven forfend, you suffer an accident or other health emergency that means you have to be repatriated. And they are only concerned with health matters, whereas a good travel policy will cover you for losses arising from such misfortunes as flight cancellations, lost baggage or a stolen passport.
You should carry an EHIC card in any case. You may want to avail yourself of the state-run medical services even if you do have insurance, and many policies won't impose the excess (=deductable) if you avoid using a private doctor or clinic. This is worthwhile as the excess is typically £50-75.
It is absolutely essential to read the policy wording fully before buying the insurance, or else immediately you have done so if you have a right to cancel within a certain period. (EU Directive 2002/65/EC gives those of us in the EU a 14 day cooling-off period when buying insurance online or over the phone for a term of a month or longer, such as annual travel policies.) The 'read the policy' advice is important for everyone, but particularly so for cyclists as cycle touring or even any bike-riding at all is excluded on some policies, and this isn't always apparent from the policy summary or 'key facts' document. Mountain biking, if it is covered, will generally require pre-authorisation and an additional premium to be paid.
Pre-existing medical conditions
Also look out for exclusions covering pre-existing medical conditions. Some underwriters require you to notify them in advance about any such conditions, and an additional premium may be charged if they then agree to provide cover. A simpler approach that other insurers take and that will suffice for most people taking short trips is to apply a blanket exclusion to any pre-existing conditions, without the need to pre-notify them. As long as you feel confident that, say, your visit to the doctor 6 months ago to get a prescription for the latest hayfever remedy isn't going to have any bearing on your forthcoming bike tour, then a policy of this type will be suitable. But err on the side of caution as insurers have a reputation for relying on the small print to resist claims.
Cover for your bike and possessions
A travel policy will cover your belongings as well as yourself, but you are unlikely to find cover for things left on your bike while it is unattended. Keep valuables in a small saddlebag or backpack and take them with you when you have a break. Nor will a travel policy cover the bike itself, for that you will need to arrange cover under your household contents insurance policy or through a specialist cycle policy. If you are hiring a bike, be sure to check what your liability is if it should be stolen or damaged and take out insurance if necessary.
Independent traveller policies
Another important thing to be aware of is that some cheaper policies are better suited to package tourists than those who organise their own tours. If your flight is delayed for 6 hours and as a result you have to cancel pre-booked accommodation and spend your first night abroad in an expensive airport hotel, you may find that the cancellation fee and the additional cost of the hotel cannot be claimed for. Certain policies are aimed at independent travellers and do cover this type of knock-on loss, and you may want to choose this type of premium product if you are going to pre-book accommodation, bike hire or other services.