My account with another provider is active until the 1st June. Assume I hang around for someone to pick this up and act on it?
Just rung my old number and it is still active (ringing anyway), so hope the port can be done.
Does this mean that you have contacted your old provider and given them notice that you are leaving? If the answer is yes them I am afraid you have stopped the port from happening. As per OFCOM regulations a number port can only happen for a valid number and there absolutely must NOT be any sort of pending cancellation request on it.
The only thing I can suggest is that you call your old provider and cancel the cancellation, even if it does mean paying them for another month or so. Once that is done, then VM might have a chance of successfully porting the number which will also cause the old line to be cancelled.