When her husband’s death leaves her desperately in debt, an English widow (Brenda Blethyn) and her now-unemployed gardener (Craig Ferguson) turn their green thumbs to cultivating marijuana. Director Nigel Cole’s film, written by Mark Crowdy and co-star Ferguson, is a bid to be this year’s Full Monty. It’s in a tradition that goes back to the Ealing Studios comedies of the 1950s, with eccentric characters, quaint provincial settings and situations that spiral off into sly, deadpan farce. Cole never quite finds the right tone, and he stumbles over some of the lurches in the plot, but the charm of Blethyn and Ferguson makes up for a lot. A scene in which two prim spinsters inadvertently get stoned on pot tea may be a bit creaky, but Phyllida Law and Diana Quick are so funny it doesn’t matter.