I belive some of the charter companies go to the Canaries twice a week. But generally speaking, all the charter companies seem to operate in/out on the same days of the week. I believe many go to LPA on Saturdays and Wednesdays, but I stand to be corrected.
So, if Sat to Wed is not convenient, you could go direct by charter one way, and come back on scheduled via somewhere else, either via Madrid or 'Island Hop' to TFS for instance.
You could go from LHR to LPA via Madrid - LH seems to have some flights operated by British Midland / Spanair. You'd have to spend a bit of time in Madrid for the connecting flight though. Iberia and Air Europa does some via Madrid, too.
[This message has been edited by Bird Strike (edited 27 January 2001).]