Can I join in? The Concise Oxford gives inquire as the preferred spelling, from the Latin Inquirere, to seek. Enquire has inveigled its way in from the French enquirer. Put it another way - has anyone heard of 'enquisition'?
For once, the Americans are right. The argument about 'in -' or 'en -' has been going on for years, but the Concise Oxford follows the OED, which is the arbiter on English spelling and which describes 'enquire' as 'half-Latinized'. Fowler also supports 'in-'