Probably the fan motor.
Simple enough to replace so long as you work carefully and methodically.
HINT 1) Make sure you know how to re-set any clock or timer after interrupting the power. Find the manual (probably available online. Search) and read it, if necessary
HINT 2) ISOLATE THE COOKER BEFORE STARTING WORK
HINT 3) Make drawings as you go DO NOT RELY ON MEMORY
These may help but check the part is correct before ordering:
http://www.rangemaster-spares.co.uk/cooker-oven/fan-motor-assembly/product.pl?pid=1233729&path=156166
http://www.espares.co.uk/product/es659058/oven-fan-and-mounting-plate-assembly
http://www.partmaster.co.uk/rangemaster/cooker-oven/fan-motor-assembly/product.pl?pid=1233729&shop=rangemaster&path=156166
XXXXX, November 2015