Heathrow overnight layover - claim and recheck luggage/go through Immigration?

Question

I am flying Cathay Pacific from Stockholm to Hong Kong with a 23-hour layover at London Heathrow. I booked the flight as a single ticket on the same itinerary (with the same booking reference). Both legs are Cathay Pacific flights. Given the overnight layover, I will stay a night at the hotel outside of the airport, prefer not to take my luggage with me. I am a US citizen.

1. At Stockholm, can I have my luggage checked through to the final destination Hong Kong?
2. At London Heathrow, do I have to claim and recheck my luggage?
3. At London Heathrow (before leaving airport), do I have to pass through UK Immigration?
4. At London Heathrow (returning to airport for connecting flight), do I have to pass through UK Immigration again?
5. At London Heathrow, how long would the security check take in general?

Answer 1

I'm fairly sure your leg between Stockholm and London Heathrow won't actually be operated by Cathay Pacific, but will instead be a CX flight number on a BA (British Airways) flight. However, that won't make much difference, other than meaning that whatever happens you'll have to change terminals (BA from Stockholm arrives into Terminal 5, Cathay use Terminal 3)

Tackling your questions in turn:

1. If you want, since it's all one ticket, they will happily check your bags through as far as Hong Kong. They should be fine to also tag some bags to HKG, and short check one only to Heathrow, so you can take things out during your layover

2. See #1. It's up to you. If you ask them to check it all through, it'll all go through. If you ask them to short check one or more bags, then you'll have to collect those ones and re-check them later

3. If you want to leave the airside of Heathrow, then yes, you will have to pass immigration to enter the country. Nothing special here with Heathrow, as a general rule to exit the airside of an airport means passing through immigration

4. Immigration is for entering a country, so there's no Immigration when you leave! Some countries have exit checks, but the UK does not

5. To be on the safe side, plan to arrive at Terminal 3 around 2 hours before departure, especially if you want to drop some bags off that you've used during your layover. Heathrow Security is often annoyingly bad (in most senses), but if you allow 2 hours then you've time for delays with getting to the airport, getting through security, finding the gate etc