Do separate tickets satisfy the UK's DATV transit requirement for an onward ticket?

I'm trying to travel to Nassau, Bahamas from Colombo, Sri Lanka with 1 connection in London Heathrow.

I am concerned about the "onward" ticket requirement in the DATV transit visa requirement. I think they will not grant it if I am on 2 separate tickets.

I can't seem to get it all on one itinerary. I can see there are flights in February on flightconnections.com but when I searched google flights and ITA, I can't find that route on a single itinerary. I would rather not use a travel agent.

Is this a concern? Is it important to book as a single itinerary?

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Do I need transit visa for connecting flight in UK?

You might need a Visitor in Transit visa if you're: changing flights in the UK on your way to another country. going through UK border control, for example to check in your luggage for a connecting flight. leaving the UK within 48 hours.

Does UK ask for transit visa?

You might need a visa to pass through the UK in transit (on your way to another country). Check if you need one before you apply. To get a transit visa you must prove that: you'll be in transit to another country, with enough funds and the intention to travel on.

Is a UK transit visa multiple entry?

You should issue a multiple entry 'transit visitor' visa valid for 6 months (long-term 'transit visitor' visas are not available). The length of leave for 'transit visitors' is 48 hours.

What is landside transit?

Landside transit refers to passengers who arrive at one UK airport but are catching an onward flight from another UK airport or who may have to re-check-in baggage and therefore need to pass through border controls and enter the UK.

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