Hi folks. I am traveling from Pakistan to Canada via a connection in the UK. Will arrive at Gatwick but have my flight onwards to Toronto taking off from Heathrow. I do have valid visa and everything for Canada. Just checking if I will need transit visa since I will be changing the airports? The airlines is British Airways only, so not entirely sure if I need to transfer the luggage either. Can someone please help?

I looked at the website and it says "you may be eligible to transit without a visa if:

• you arrive and depart by air
• have a confirmed onward flight that leaves on the day you arrive or before midnight on the day after you arrive
• have the right documents for your destination (eg a visa for that country)

One of the following must also apply:

• you’re travelling to (or on part of a reasonable journey to) Australia, Canada, New Zealand or the USA and have a valid visa for that country"

I do meet the above conditions, but is it something the immigration officials will decide on spot? Do these things not apply in cases of change of airport?