I have just travelled back from IAH > LHR

I was travelling with 2 work colleges , one bronze status the other has just achieved silver status.

One was upgraded at check in , the other upgraded at the gate.

I have been a silver holder for 5 years and was not upgraded.

I would of though there would have been some weighting in the tier's and length of activity (been with BA for over 20 years)

Does anyone have insight and care to share ?