Actually, a surprising number of British aircraft manufacturers survived the transition to peacetime: Avro, Armstrong Whitworth, Beardmore (although aviation was more of a sideline than a primary business), Blackburn, Boulton Paul, Bristol, Fairey, Gloster, Handley Page, Parnall, Shorts, Vickers and Westland.
As previously noted, Sopwith went under but re-emerged as Hawker Aviation. Similarly, Airco went into liquidation but its assets became the De Havilland Aircraft Company in 1920. Pemberton-Billing Ltd became Supermarine shortly after the war, perhaps in an attempt to distance the company from the awful aircraft designed by it's founder Noel Pemberton Billing.
Companies that went under included British Aerial Transport, Grahame-White Aircraft Co., Martinsyde, Tarrant Ltd, and the White & Thompson/Norman Thompson Flight Company.