B Meow, on 2015-January-23, 08:47, said:
Would the rebid been
1♦ P 1♥ P
4♦ P ...
Had the opponents not interfered?
This would promise a fourth heart.
Quote
BTW it is legal to make this as 2♣ opener. Given an extra diamond, many pairs would have a 2♣ opening.
Yes, in the ACBL as many have explained. Of course the OP is in the UK, but who cares about such trifling details.
In any case the fact that it is legal does not mean that it is the right choice.