Sorry for the silly sounding question but I don't have a tool to turn this - what type of screwdriver style slot is this called please so I can make a useful trip to Halfords?
Much appreciated - thanks for the help. Clearly admitted this must the the first time I've fettled anything major on the bike given I haven't undone one of these yet!
Sorry for the silly sounding question but I don't have a tool to turn this - what type of screwdriver style slot is this called please so I can make a useful trip to Halfords?
Like the guys above rightly mention, its called a 'torx' bolt. You should be able to get a set of varying size keys to remove the stud.
Just make sure you get the right size key as it is sometimes easy to damage the shaped area in the bolt head if you do not, also ensure it is free of muck and grit to ensure the key sits fully in the recess.
Most decent motor factors will have what you want in allen key type thingies or socket type heads.