I had a similar issue; in fact I`ve had several temporary outages over the last week. In all cases there were BT core network faults stated on Zen`s status website (status.zen.co.uk) when my connection was down.
I did speak to Zen technical support about my issues, but strangely they seemed ignorant about this status webpage, which is worrying, and instead had me check my own equipment, use the test socket etc etc
All has been OK however, since 6.30pm yesterday. Fingers crossed it stays that way!