Think they shorter, wider and deeper (almost squarer) than the generic rocker switches in Halfords
Sure you've alrady considered this, but as they are easy to take out (2 screws and a pull off connector) I'd just take one to hold against one in Halfrauds - or of course buy one (They're less thans £5) and take back if it's wrong.
Suspect a Halfords one could be made to fit, but may not look quite right alongside the others