frame builders

Morning all Well, any ideas what this might be? Stamped with four numbers and an ‘O’ or 0 separately on the bb Oil port, sharp rake, nice components, some of which look contemporary with the frame, others a top of the line set of early ‘60’s upgrades Arrived to be in Hammerite Blue, all original...

Found an interesting FW Evans frame. It has quite nice lugging and unusual seat bolt position (I’ve only seen that on Roberts bikes. Does anyone have any information who the frame builder could be? Appreciate any information. Thanks