Can you help me set the clock

Check your breaker panel or fuse box to see if something is tripped. If you have a breaker panel, try flipping the stove breaker off all the way even if it looks like it is still on and then turn it back on and check stove. If you still have no power then you probably better call an electrician.

What is the model number of the unit?

replace fan unit

Most of these timers have 3 buttons, the hand and the plus and minus buttons. Try pressing the minus and plus buttons at the same time. The display should flash. Then adjust the time with the plus and minus buttons. If this doesn't work just try different combinations of pressing 2 buttons. If the timer is not faulty on of these combinations will work.

http://www.rangemaster.co.uk/Siteimages/Site_311/Pdf/ProfessionalPlus110DFOct08.pdf
User manual.
When the clock is first connected, the display flashes ( 0.00) and (?) alternately. To set the time, turn and hold the Timer knob to the clock symbol (?) and at the same time turn the Adjusting knob left or right until the clock shows the time of day. Remember this is a 24-hour clock. Let go of the Timer knob and it will spring back to the vertical, oven manual setting.
It is on page 6 of manual

apart from a faulty clock. a thermal cutout may have tripped due to an overheat (either a long days cook or a faulty thermostat...) would be best to get a pro in to sort out as this is a duel fueled unit & entering the gas domain it's best safe this time of year... sorry

Emmet in luton: what fuse does a rangemaster 90 duel fuel need?

vinigar might work

Yes this is easy to do.We can supply bits if required.

Comes on like this when switched on, hold down the left 2 buttons on the clock controls then whilst still holding them pres the right hand button

or manuals available here...
http://www.rangemaster.co.uk/index_Rangemaster_Manuals.htm