From the installation manual which is at partsarena.com\baxi:
6. Turn the boiler thermostat to the "OFF" position.
7. Turn on the mains electrical supply.
8. not for you!.
9. Hold in the grey button on the gas control valve (Fig. 7).
10. Press the Piezo unit button and release. Repeat until the pilot lights. Hold in grey button for a further 15 seconds and then release. The pilot should then stay alight. If the pilot fails to remain alight twist the grey button clockwise and release wait three minutes and start again from 9.
It's all underneath at the front, behind a flap/panel.
NB if the place has been empty a while it'll have air in the gas pipe and take forever to "purge" through the boiler pilot, so light the fire first
if you dont know the boiler or its history you could be well advised to get the whole thing checked over by an engineer, he will check the vents, service it and ensure you dont have any probs ( i would also suggest fitting a CO alarm as well) Glasgowgas and Tonybhoy are both local to you they might help, i'm in coatbridge but i'm sure they will dive on and offer to relieve you of a few quid