Paul Corfield wrote

This is fair enough too. The other issue though is whether you really
want to lug you and your belongings off at Hatton Cross and then back
on
again when in reality you might "waste" all of 8 minutes by staying
on
the train and going via T4. Personally I'd prefer to stay put but
then

On a related question, the 555 from outside my home is routed Terminal
4, Hatton Cross, Heathrow Central Bus (terminates).

If I am arriving at Terminal 1 or 3 is it worthwhile to take the train
to Terminal 4 and catch the bus there (or the reverse when departing) ?

--
Mike D