Visa requirements for British Nationals are detailed on the Foreign & Commonwealth office website ww.gov.uk/foreign-travel-advice It is necessary to check the visa conditions carefully. In some countries it is necessary to have vacated the country by the end date of the visa. In other countries it is only necessary to enter before the expiry date and it is then possible to stay for the maximum stay permitted by the visa. The caravanistan website www.caravanistan.com/ provides comprehensive travel and visa information on central Asia. I did not find this site until part way through my trip. If I had done so I would have known that it is only possible to get Pakistan tourist visas from your home country. Uzbekistan:- I was granted a visa much shorter than the duration I requested. Online reports show this is quite common. When applying for a visa you have to fill in an online form and put ticks against the places you plan to visit. All I can suggest is that you put ticks in a few extra places to make it appear you are travelling further than is actually the case. That way you should be able to get a bit of contingency.
Myanmar: The Myanmar visa was easily obtained in London before I departed. In order to leave via the land border to India at Tamu/Moreh a permit is required. When I entered Myanmar at Tachileik, I discussed my route with the border officials. They said, that as I was on a bike and not a car I should be OK without a permit. As I cracked my rear hub part way up Myanmar and had to head carefully instead to Bangkok I did not get to test this theory. When I was in India I met a fellow cyclist from the Czech Republic that had got across this border post and he had obtained a permit from a travel agent in Rangoon.
Iran – When I visited during 2016 British Nationals along with Americans and Canadians on tourist visas were only allowed to visit as part of an organised tour that has been approved by the Ministry of Foreign Affairs. (MAFA). The tour agent provides details of the tour itinerary to MAFA who then (for a fee) issue an authorisation number. This is then used to apply for a visa. There are Travel Agents that can arrange paperwork for individual travel. I found a link on hitchhikershandbook.com to a travel agent that has since been removed. It will be necessary to email several travel agents and see who will obtain a MAFA number where the tour guide is more virtual than actual. My agent obtained the MAFA number in return for booking a 1 day guided tour plus the MAFA application fee. Most people report that they have not been challenged on where the tour guide is when entering the country. If asked just say you are meeting them at the hotel. I applied for my visa in Dushanbe. When I made my application I was told to return the following day and had a short interview. The Embassy staff were very hospitable and provided me with tea and Turkish Delight. When I was asked why I wanted to travel in Iran I stated that I had previously worked on the construction of Tehran metro and wished to see it in full operation and provided a copy of my old visa. They said that this was fine and issued a business visa the following day that allowed me to travel independently totally legitimately. There was some brief questions on the route I intended to follow and what I thought of Iran from what I had read in the media, but nothing that would suggest they were looking for reason to refuse issue of a visa. I made no mention of intending to cycle in my application.