Hi there richteab, as many have pointed out the answer is not a straight one as there are many different variables (transfer/direct, type of lounge, type of service). For the IT-inclined of you all, there is/was a data table that provided minimum travel times between different touchpoints in the customer journey, and it is/was used to calculate conformance. It had hundreds of combinations.

Anyway, the rough and ready is, in my view and experience (tuning down the estimates to account for a slower pace) and being conservative:

1. For direct (i.e. front-of-house) passengers:
   1. If using the first wing, from check in to CCR/GF lounge I'd say 15 minutes (more if there's a queue at security).
      1. From there to any T5A Gate, between 15 and 30 minutes
      2. T5B, 30-40 min including using the train
      3. T5C, 45-50 min including using the train
   2. If not using the first wing, from the North side of check-in to Galleries North I'd say 20 minutes (more if there's queue at security)
      1. From there to any T5A Gate, 15-30'
      2. T5B, 30-40 min including using the train
      3. T5C, 45-50 min including using the train
   3. If not using the first wing, from the South side of check-in to Galleries South... I wouldn't probably bother if walking is troublesome. You need to go down a level and then back up again. It can take a good 30/40 min for a slow walker
2. For transfer passengers, oh, too many options here and we'd need a bit more data (i.e. coming from where and so on).

Some might suggest assistance. At LHR, I wouldn't go for it. Unless it's really a case of not having other options.

In this case I think it's point 1.2.1 or 1.3.1 for you. There's still the chance that the flight to Rome leaves from T5B or C though shorthaul flights normally depart from A (on-pier or remote).