https://en.wikipedia.org/wiki/List_of_Air_Ministry_specifications
P.13/36 OR.41 Twin-engined medium bomber for "world-wide use" introduction delayed due to production difficulties necessitating further order of Whitleys & Wellingtons
Avro Manchester (2 prototypes ordered), Handley Page H.P.56 (one prototype ordered), Hawker P.13/36 (project only), Vickers Warwick with Rolls-Royce Vulture engines
According to BRITISH SECRET PROJECTS FIGHTERS & BOMBERS 1935-1950,
Following proposals are included.
Avro 679, Boulton Paul P.91, Bristol P.13/36, Fairey P.13/36, Handley Page HP.56, Hawker P.13/36, Short P.13/36, Vickers P.13/36,
Avro 679 Manchester, Handley Page HP.57 Halifax, Avro 683 Lancaster and Avro 684.
Vulture engine.
https://en.wikipedia.org/wiki/Rolls-Royce_Vulture
Avro 684.
https://www.secretprojects.co.uk/forum/index.php/topic,642.msg314687.html#msg314687