For £200 I would get an SB600 or if you are lucky pick up a 2nd hand SB800 or SB900 (both not that likely at that price point).
If you can find the extra for an SB800 or SB900 they are worth it but the SB600 is still a great flash, I use one daily in my job then come home to the SB900
Some may groan but Ken Rockwell has done a few reviews re Nikon flash units. Have a read you may find it informative, take a look at the SB400.
http://www.kenrockwell.com/nikon/index.htm#flash