Viscount, you make this a very interesting point! Since you asked I went to look at the books and - where it is written down - it's written in reverse, if you see what I mean.
The only absolute in the Manual of Air Traffic Services is 'Unless specific procedures have been approved by the CAA, a landing aircraft shall not be permitted to cross the beginning of the runway on its final approach until a preceding aircraft, departing from the same runway, is airborne.'. In this context I think 'permitted to cross' means allowed to continue (i.e. not given a go-around) rather than been cleared to land but others may have a different interpretation.
There are other bits in the Manual that say things like 'Clearance to land or alternative instructions received from approach/aerodrome control shall be passed to the aircraft before it reaches a range of 2 miles from touchdown.' This is specifically about radar vectored instrument approaches and, in practice, alternative instructions can include to continue approach.
The law says ‘air traffic control clearance’ means authorisation by an air traffic control unit for an aircraft to proceed under conditions specified by that unit (Rules of the Air Regs). 'Continue approach' is an authorisation by an air traffic control unit. If there is no ATC, the general rules for avoiding collisions etc apply, one of which says 'A flying machine or glider shall not land on a runway at an aerodrome if the runway is not clear of other aircraft'.
The reason I gave the original answer was because that's the way I was taught to do it on simulators and when doing on-job-training. Given sensible application it works and it's safe - but it doesn't seem to be written down anywhere, although I do recall a little training book that may have given more details.
You ask if a minimum height is written down anywhere that says an aircraft must go-around if it doesn't have a landing clearance. In the UK, I don't think there is although as I said earlier, some aircraft operators might specify one for their aircraft.
The nearest I can think of to what you're looking for is the 'approach ban' that says an aircraft shall not descend through 1000 ft when making an instrument approach if the relevant runway visual range is less than the specified minimum for landing.
Hope this helps.
Last edited by Spitoon; 27th Jan 2003 at 19:36.