1. I have a British friend who uses 400K on deposit and his pension to satisfy the "retirement extension" requirement. However, he informs me that every 90 days - as well as reporting - he has to provide a letter of proof of his pension which he needs to get from the British Embassy in Bangkok. Being as he doesn't drive - and lives over an hour outside the city, the only way he can get this is by taxi. He had a career in logistics and worked for some lucrative projects in London, China and Hong Kong, so it's a pity that he didn't save his money.
2. I myself am only on a partial UK retirement pension (that doesn't increase as everyone knows), so the 800K is my only option.