LATER NOTE: This edition is the 2002 edition with a new cover. Moreover, the quotes from the TES and TLS given on the original cover are now both ascribed to the TES. Conclusion: a waste of money!
There is a 2003 edition of Elizabeth Martin’s Oxford Dictionary of Law. This is a relatively small paperback, price £9.99. In its first edition it was called Concise Oxford Dictionary of Law, but later they dropped the ‘concise’. As there’s no British equivalent to Black’s (USA, especially Garner’s 7th ed.) or Creifelds (Germany), I prefer this. There are other dictionaries of the same size, such as Mozley and Whitely or Curzon, which tend to have more and briefer entries. I should make a special reference to Chambers, because that has a surprisingly large number of entries on Scottish law.