I hold a Ghanaian passport and possess a valid Canadian visa. My travel plans involve a round trip with British Airways from Ghana to Canada, with layovers of 8 hours each at Heathrow Airport in London, both on the outbound and return journeys.
Given that my intention is solely to transit through Heathrow Airport without exiting the airport premises, I am seeking clarification on whether I require a transit visa or any other form of visa for this travel arrangement.
You will be able to stay "airside" (i.e. avoid going through passport control) when you change flights at Heathrow. Therefore it's a question of whether you are permitted to make an airside transit without visa (TWOV).
The UK Government website has a helpful overview of transit visa options (including TWOV). They have a tool you can use to check whether you need a visa for your specific situation. Depending on how you are planning to enter the US, it's possible that you do not need a transit visa.
However, it's worth noting that the above only tells you (on an informal, non-binding basis) whether the UK Government considers you eligible for an airside TWOV. You also need to check whether your airline agrees with this view - if they don't agree, they will deny you boarding on your first flight and your reservation will likely be cancelled.
The easiest way you can check the airline's view is to use the same system that their staff will use to check your TWOV eligibility: this is called Timatic (it's an industry-standard system developed by IATA). You can access this on several airlines' websites, e.g. Vistara here.
Even if Timatic is wrong, ultimately this is what the airline staff will go by - so you can only conduct a TWOV if both the UK Government and Timatic agree you're eligible for TWOV.
Based on the information I can see, you will be eligible for a TWOV through Heathrow if you have a visa for the Canada, New Zealand, Australia or the USA. But I am not an immigration advisor, so you may wish to speak to your nearest British Consulate to confirm this.
