Thank you for all your help everyone, appreciated!
We were delayed on the ground in Jersey to weather and late arrival of the aircraft.
Once we borded, we were informed that there would be a 15 minute delay until take off due to delays at Heathrow (or similar reason).
Once we were close to Heathrow, we were told that Heathrow had put us in a holding pattern (5 minutes).
After all the delays, we arrived into LHR pretty much on time! 😂
I made a mad dash through T5A to go to T5B and from leaving the plane to being at T5B took 20 minutes at most, probably 15 as the train arrived just as I was going down the escalator, despite people not standing to one side. Heathrow, put some signs up!!!
When I got to T5B, they had not even boarded anyone! They seemed to be 10 minutes late. They had started to segregate and process families and 'infirm" to sit at the gate.
So as I had time, I went to the lounge for 10 minutes and when I came down, they had started the boarding process.

Excellent flight,flighd in the IFM as my dedicated crew member and he was excellent.