Easiest (only?) solution is to buy a clock from Gas on Spares (see below), which costs around £100, and fit it yourself - this is easily within the reach of anyone who can handle a screwdriver. 
If you're not sure how to get the top off the cooker to gain access to the clock, call someone at Rangemaster - they're vvery helpful
 
(Gas on Spares - Tel: 0800 3890907
Email: gason@btconnect.com
Website: http://www.gasonspares.co.uk/
                
 Nick and Daniele
                
 September 2007