In a GAAP if you are sequenced and it ain't going to work, request to make number one to the other aircraft. Majority of the time it is then a simple case of saying approved and telling the other aircraft they have been resequenced and follow the XXX overtaking on your right/left (as the case may be). Obviously there may well be occasions that you can't be resequenced for whatever reason so you might find you are trying to follow or going around and making another circuit. However if you don't ask you may well find yourself going around from base or final anyway.