Re: Cleaning my 147
Up to you what you're looking for. As tcm says you could take your car cleaning to the umpteenth detail and spend hours detailing to drive it in the rain and get it all grubby again.
My routine: A bottle of car shampoo, bucket and sponge from Halfords does the trick with a hoover out once every couple of weeks. Polished/ waxed with Mer and a good inside spring clean every 6 months.
Don't use washing up liquid. It's not good for the paint but you don't need to spend a fortune on shampoos and potions either, Autoglym, Simoniz, Turtle Wax bubbles are all good and not too expensive: £3 - £5 a bottle, any more and you're into diminishing returns, budget brands don't do the job as well. Don't be foolded by marketing and the sales guy in the shop telling you you will need different bubbles to do the alloys, another one for the tyres, one for the bumpers, a separate one for the glass, one for the interior, one for the upholstery ....
It all depends on your budget and how much time you've got. I wouldn't let anyone else wash my car because I have a principle of not paying people to do something I can do myself and I know I do a good enough job for my standards but I'm not going to spend hundreds on potions to get it gleaming until I drive it in the rain.
Up to you, can't go far wrong with car shampoo, bucket and sponge IMO