it looks like a leech what is it

Probably a slug

Yuk!

the only creature that you need to worry about is the New Zealand flat worm which is a problem for our garden worms. try googling for pics

Even the flat worm isn't proving the problem it was first thought to be. The worm populations in areas that have flat worms are returning and the flat worms are dying off... at least that is what is happening in our neck of the woods.

Cams: the new zealand flatworm was first discovered in 1963 in Ireland so I wouldnt be surprised if this is what your creature was as they are now endemic there.
moon grower i think if you do a search of the literacy you will find that there is still some concern about this worm. It may not prove to be a problem in Scotland however any decline in the worm population in agricultural areas such as the south or south east could prove a problem. I would still urge anyone who has found these to report them (there is a link through gardeners world BBC)especially in the south of the country