All 'proved' wills are public documents. They are held by the probate registry. Details of how to obtain a copy of a will are here but, if at all possible, I'd suggest a personal visit to one of the addresses shown towards the bottom of the page;
http://www.hmcourts-service.gov.uk/cms/1226.htm
Of all the various departments of government I've ever dealt with, the Probate Office staff have been by far the most efficient and helpful, so you shouldn't find much difficulty in obtaining the relevant document.
Chris