Have you ever tried it? Took us 3 attempts and a threat of legal action to get even a visitors visa......Please do your research first without putting comments like this.
I've tried it successfully on a number of occasions.
Heck of a difference between someone getting a visa to visit the UK and someone trying to get a transit visa.
The people who grant the visa are UKV&I - part of the Home Office. Surely the best thing to do is contact them and get the answer in writing instead of giving us part of the information and changing it half way through (20 hour layover then 30 hour?).
If you want amateur advice post on here. If you want professional advice pay for it or get it in writing from those that make the rules.