What's a good mountain bike for £150 (Uk only obviously!) and where can I get one in Brighton?

Normally I would say a road bike or a hybrid for this money. However, if the trails are an issue, then hybrid or hardtail mountain bike.

You are not going to get much for the money, so rather than looking at discs or full susser (Don't recommend unless you spend about £700), then keep it basic. Simple rigid design, with V brakes. If you have forks, they will probably be 80mm cheapies.

Consider these:

http://www.evanscycles.com/products/dawes/discover...

Dawes are not bad. This is a bit over your budget, but it uses branded components and should last a few years.

http://www.evanscycles.com/products/raleigh/ventur...

This is not a bad machine for the money. It is simple with 6 speed Shimano brakes. Rigid forks and 700 road wheels, so he will feel the bumps, but will be good for quite a few miles.

http://www.evanscycles.com/products/falcon/richmon...

This is a good commute machine. Rigid forks, SRAM and Shimano components. Mudguards and, as a bonus, a rack (Useful for puting the sarnies and a change of clothes on). Falcon are the mother company behind Claude Butler. They are lower speced bikes, but are designed for people working to a budget.

Note: I have used evans because they have a lot of selection to use as an example, but not necessarily as a recommendation.

A couple of words about your bike. Do not buy from Halfords. The muppets in their workshop have varying abilities. However, for the money, they are not going to offer you much of a bike.

Do not buy from the internet (Evans is an exception), unless you know that the bike will be set up and built for you. Do not try to assemble a bike yourself unless you know what you are doing.

Make sure that he rides with a lid (Give him hell on this one if necessary). A high vis vest is viable, but if he is using this for commute, even in town, then he will need viable lights. You can make do with a set of flashing leds front and rear if in town, but if he is on the country roads he will need to see where he is going, so look at about £30 + on the front light.

There you go. War and Peace.

Luck

Look for a good used bike on the local ebay or other site. A new bike in that price range is going to be junk.

Halfords is a good place to start, there's one in Hove. Mountain bikes start from less than £100 there so you should find something decent within budget.

Look for something used. maybe eBay