Most spanish operators operate from the Canaries to the UK inc. Futura (737-400/800), Iberworld (A320), Spanair (MD83) and Air Europa (737-300/800, 757,762). Normally with uk charter airlines the larger aircraft operate to Tenerife and Las Palmas when these a/c are not operating to other popular holiday destinations. Again it depends on where you are flying from. If you are flying to Tenerife on a friday morning at around 7am , it is very likely you will get a large a/c if you fly from LGW or MAN. Around 12pm it will probably be a smaller aircraft.
When you hear the noise of the Tartan Army Boys, we'll be coming down the road!