There is no requirement to hold an instructor rating in order to give flight instruction unless it is for "the grant of a pilot's licence; or the inclusion or variation of any rating or qualification in a pilot's licence". Since a club check-out is none of these things, an instructor rating is not required. The same would apply to, for example, aerobatic training, formation flying or anything else that did not result in licensing action.
This all relies, of course, on it being a private flight. If valuable consideration is given, it becomes public transport - a whole different can of worms.