December to March, when the UK is 6°C and dark by four. The question is how far you're willing to fly for how many degrees.
That's the whole trade-off, and it's worth being honest about the middle option.
The Canaries are four hours away and sit at 21–23°C through January — genuinely warm, same time zone, and cheap. The Gulf is seven hours and gives you 25–28°C with guaranteed sunshine. The Caribbean and Indian Ocean are eight to twelve hours and give you 29°C and warm sea. What doesn't work is the Mediterranean: Spain, Cyprus and Türkiye are mild in winter, around 15–17°C, which is lovely for walking and golf but nobody's swimming.
Ranked roughly by flight time, with honest temperatures.
21–23°C, four hours, same time zone. The best warm-to-effort ratio in winter.

22–24°C and reliably dry. Five hours, and the reef is at its clearest in winter.

25–28°C, no rain, and a city attached. Peak season for a reason.
Same weather as Dubai, 20–30% cheaper on the hotel.
24–26°C and the Gulf's best scenery. Quieter and more interesting than the UAE.

29°C, dry season, and the water at its clearest. The furthest and the warmest.
29°C in the dry season, direct flights, and no jet lag worth the name.
29°C, no hurricanes, no seaweed. November to April is the window.

32°C on the Andaman coast, dry and clear. Far, and the cheapest once you're there.
The Canaries, comfortably. Four hours for 21–23°C is unmatched. For genuine heat you need the Gulf at seven hours.
Sharm and Hurghada operate normally and are heavily geared to tourism. Check the current FCDO advice, which covers different parts of the country differently — we'll go through it with you.
Slightly cooler and a bit wetter than January and February, and busy over Christmas. Still 20–22°C most days.
Technically, at about 16–17°C. Most people find that too cold for more than a quick dip.
Four hours buys 21°C. Seven buys 26°C. Twelve buys 29°C and a warm sea.
21–23°C in January, same time zone. The best warmth-per-hour on the list.

22–24°C, reliably dry, and the reef is clearest in winter.
25–26°C and barely an hour off UK time. Warmer than the Canaries.

25–28°C, no rain, and a city attached to the beach.

32°C on the Andaman coast, and the driest months of the year.
29°C and a sea that's warmer than the air feels. Peak season, priced as such.
Guide prices, per person, based on two sharing, including return flights, accommodation and transfers where stated. They indicate what a holiday of this type has typically cost and are not an offer or a quotation. Your price depends on dates, party, board basis, departure airport and availability, and is confirmed in writing before any payment is taken.
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