Landon IP provides a file history service which can deliver both paper copies and electronic file history Web Wrappers in PDF format. The Web Wrappers are free with the purchase of the paper copy.
For a GB patent document, it will cost roughly $300 USD and take about 3-7 business days to obtain. The cost and time estimate really does depend on a case-by-case basis, though. Please keep in mind that, if the file is abandoned before its publication, then the file history is not available. If a file was published but the application was eventually withdrawn/denied, the GB patent office only keeps the file for 7.5 years thereafter.
The search system Ipsum, created by the IPO, provides some documents and forms openly available from the file histories for GB patent documents.
I hope that helps!