The basics
The UK to Thailand is a seven-hour time shift heading east, and one of the harder adjustments for British travellers. Most flights from London arrive in Bangkok in the late afternoon or evening local time. When you land at 5pm Bangkok time, your body thinks it's 10am. You're nowhere near ready for sleep, but the local day is ending.
Eastbound travel is harder than westbound because you're asking your body to fall asleep earlier and wake earlier than it wants to. Expect 5 to 7 days for a full adjustment, though you'll feel functional within 3 or 4.
What jet lag feels like on this route
The main symptom is insomnia at night. You'll lie in bed at 11pm Bangkok time feeling wide awake because your body thinks it's 4pm. When you finally do fall asleep, often around 1 or 2am, you'll sleep heavily and struggle to wake up. Mornings will feel brutal for the first few days.
During the day, you'll have a window of alertness from mid-morning onwards, then a second wind in the evening that makes it hard to wind down. The cycle repeats until your clock catches up.
Appetite disruption is common too. You won't be hungry at Thai mealtimes and you'll be starving at odd hours. This is normal and resolves as your clock adjusts.
Day-by-day recovery plan
Most UK to Bangkok flights arrive in the evening. Don't try to go straight to sleep; you won't manage it. Have dinner, take a short walk, but start dimming your environment from 9pm. No bright screens, no overhead lights. Take melatonin (0.5 to 1mg) at 10pm local time. Even if you don't fall asleep immediately, stay in bed in the dark. You're training your clock.
On day one, you'll probably wake late and groggy. Get outside into bright sunlight as soon as you can. Morning light is the most effective tool on eastbound routes because it tells your brain "the day has started" and pulls your clock forward. Spend the morning outdoors. A 20-minute nap in the afternoon is acceptable if you set an alarm. Take melatonin again at 10pm.
Day two is slightly easier. Force yourself up by 8am even if you're tired. Get outside. The morning light exposure compounds: each day it shifts your clock forward by roughly an hour. You might find you can fall asleep by midnight tonight instead of 1am.
By days three and four, you should be falling asleep by 11pm to midnight and waking by 7 or 8am. Keep going with morning light and avoiding bright evening light.
Days five to seven: most people feel fully adjusted. If you're still struggling with the last hour or two, keep the melatonin going at 10pm.
What helps
Morning sunlight is the number one tool on this route. Get outside before 10am every day. Even 30 minutes of natural light makes a measurable difference to how fast your clock shifts.
Avoid bright light in the evening. This is counterintuitive in Thailand where the nightlife is part of the appeal, but bright light after 8pm tells your brain it's still daytime. If you're going out, sunglasses in brightly lit areas can help. Yes, at night. It works.
Melatonin at destination bedtime (0.5 to 1mg, 30 minutes before your target sleep time) supports the shift. Don't exceed this dose. Higher amounts cause grogginess and don't speed up adjustment.
Stay hydrated. Bangkok's heat combined with long-haul dehydration compounds fatigue. Drink more water than you think you need.
What to avoid
Don't sleep until noon on your first morning. It feels kind, but it anchors your clock to London time and extends the adjustment by days.
Don't rely on alcohol to help you sleep. Chang beers on Khao San Road might knock you out, but alcohol-induced sleep is fragmented and counterproductive.
Don't take sleeping pills for more than one or two nights. They can mask the adjustment and leave you dependent on them for the whole trip.
The return trip
Coming back is easier. You're heading west (Bangkok to London), which means you're delaying your clock, a more natural direction. Expect 3 to 4 days of adjustment. The main symptom will be early morning waking (4 or 5am UK time) that gradually shifts later.