Can I protect my second ticket from the cancellation of a separately purchased first ticket on a connecting flight

You bought separate tickets. That means Qatar doesn't even know about your first flight. It is your personal duty to make it to Heathrow with enough time in-between flights to allow for rechecking bags and going through security. Or in other words: this is not a connecting flight.

Your best option in terms of security would be to rebook so that both flights are on the same ticket/PNR. In that situation, it is the airline’s responsibility to get you to your final destination, and in case there is any disruption they will rebook you as soon as possible and take care of you in the meantime (that can include hotels and meals if you are stranded overnight for instance).

The other big advantage is that you would be able to through-check your luggage to the final destination, so you don’t have to worry about it in Heathrow (and that makes the minimum connection time much shorter).

If you still want/need to travel with separate tickets, remember that you need to budget enough time to:

• Deplane
• Get to baggage claim, wait for your luggage
• Exit the arrivals area, go to departures
• Check-in/drop your luggage before the check-in deadline (one hour before departure)

If all goes exactly according to plan, 2 hours between scheduled arrival and departure should be plenty (same terminal, no immigration…). But things can go wrong, with flights delayed or cancelled, luggage not loaded or unloaded timely (if at all), and so on.

If you miss the check-in deadline for your second flight, you’ll be considered a no-show, and for most fares, your ticket will be cancelled (possibly including further flights on the same ticket).

You would the be on the hook to book and pay for new tickets at last minute prices, which may be a lot more expensive.

To mitigate this, one option is to buy a more expensive “flexible” ticket which may allow you to cancel or change your second flight if needed. Note that there can be complex rules about this (including having to cancel or change before departure, or even a few hours in advance), there may be fees/penalties for doing so, you may have to pay the fare difference (again, based on last-minute prices), and there may be different levels of flexibility, at different prices. Fully flexible tickets are usually very, very expensive.

Another option is to purchase travel insurance. Again, this is not an easy task, with lots of options and details. Missed self-connections are unlikely to be covered by the cheaper policies, you may have to select more expensive policies or add options to get it. They will come with lots of conditions, probably including a minimum time gap between the two flights which may be quite a bit larger than you would expect. Read the small print carefully, make sure the policy actually covers self-connections, and covers all the cases you can think of (see above for a few ideas).

Yet another option is to have a gap large enough that you are unlikely to miss your second flight. If you were travelling in the other direction, the rule of thumb of 4 hours should do it: in the rare case you would be delayed so much you would miss your second flight, there are still enough options which should be affordable that you can pay for a new ticket.

In that direction (short-haul connecting to long-haul, where the second flight is significantly more expensive), a larger gap is a good idea, and many people would advise to arrive the day before, stay overnight, and be ready for your second flight the next day in nearly any event.

You can of course combine several of these options. But again, your best bet is to have both flights on a single ticket.