How do I rent canal boat in the UK?

If you specifically mean a holiday on a canal narrow-boat, you need to do some research into your planned route. You can get advice, maps, etc, from the hire company.

Bear in mind that the maximum legal speed is 4 miles per hour, and most hire boats will not exceed that my much even if you disregard the law. Also, you need to allow time for going through locks, which is one of the "most fun" parts of the experience of course. At busy times in summer you might be waiting in a "traffic jam" of boats at a lock for a long time (i.e. an hour or so).

If you are over-ambitious about the distance of your planned trip, you may have real problems. You can't "turn round and head back home" any time you want, because for much of the time your boat will be longer than the width of the canal! In some parts of the canal system, travelling 10 miles in a day would be good progress. There are horror stories of people travelling all night in reverse, to get back to base on time. Don't go there!

Canal boats typically sleep 4, 6, or 8 people depending on the size (length) of the boat. If you have unused berths, obviously the cost per person will be higher. The practical minimum number of experienced people to handle a boat is 2, but that's hard work, and a minimum of 4 "beginners" (not counting children younger than teenagers) is better.

The boats were designed to carry 20 or 30 tons of bulk cargo like coal. The hulls are steel, not fiberglass. Don't be scared of damaging them - they bounce off most things pretty well ;-) If you get into real trouble, somebody from the hiring company will come and sort you out.

Final tip: if you can, take some bikes on board. You can save time if somebody bikes up the tow-path to the next lock, sets it up ready for the boat to go straight into it, and the boat doesn't have to wait while you close the lock gates behind you, etc. Bikes are also useful for short trips away from the canal to shops, pubs, and such like. If your is group big enough, some people can take a day exploring the local countryside on bikes and meet up with the boat again in the evening.