I can recommend two carpenters who I have known and worked with for years.
First one is Terry Murphy. He is actually a cabinet maker and can do any job really well at a reasonable price. His number is 02087780136. Its his home number so its best to call after 6pm(he is old-fashioned and refuses to get a mobile). The other is John, on 07752419880. He too is reasonable. I have been plastering for twenty years and know a good tradesman when I work with one.
A bit of advice if you are unsure about getting building work done. Get three quotes to get a rough idea of price. If you get a really cheap quote BEWARE. In building you get what you pay for (usually). Pay cheap and you pay twice. I have had to re-do hundreds of jobs where people have thought primarily about the cost rather than the quality then ended paying twice as much as they needed to.