I leave my car at work so have to cycle in. My back up plan is to wake the wife and ask for a lift

Motivation enough to get on the bike.
The rewards - dawn chorus, blue kingfisher at the river, no traffic hassles, exercise done for day and a sense of happiness/contentment. Why would you need motivation.
You could also take the Sean Kelly approach:
David Harmon once asked Sean Kelly was the weather ever too bad for him to train and he replied, in his inimitable style, "well, David, I'd always have gone out anyway, and decided afterwards whether it had been too bad..."