Some counties allow for referees to do the 'double jump' (London being one of them). Basically it means that in one marking season (March 1st - February 28th), referees have the ability to complete 2 (or 3) promotions in one go.
To go from 7-5, a referee will have to complete 40 matches within the season (20 between March and October, and 20 between October and February) and be assessed 6 times (3 between March and October, and 20 between October and February). As well as this, they also have to complete the two exams (7-6 and 6-5) at in-service training events. If a referee going for promotion has an average of greater than 73, then the County FA may also nominate them to the FA for promotion to level 4 - effectively meaning they have had 3 promotions in one season. Providing they have completed the relevant fitness test and have also attended one of the FA seminars where an additional Laws of the Game assessment is sat.
If you want the opinions of users of the forum, do a quick search. It has been discussed many times before with the general consensus that the older 'more experienced' referees don't agree with it, whilst the younger referees seem to think the idea is a good one, allowing them to progress up the ladder more quickly.