IMO they are likely from Dovedale. I had a set many years ago in the form of the Unit 5 kit which was the "build yourself some Dovedales" kit from around 1971 and had been built up very professionally to the larger of the two cabinet sizes given in the plans (larger than standard Dovedale). The builder had made a plinth as part of the cabinets which raised them about 3" so overall a large speaker. They were probably made around 10-12 years before I got my hands on them. There was a paper coned midrange of about 3-4" and that nasty purple plastic dome tweeter. They actually sounded good. Tight bass from the sealed box, decent midrange and as the purple tweeter didn't have to go too low when used with a mid driver it wasn't too bad in this instance. I recall them sounding bloody marvellous used near field, about 1m away and speaker inner edges only about 1m apart with a youthful me sat on the floor with ears about midrange driver height. Around '85 ish I gave them to my late pal Tony who was about 20 years older than me and a lifelong avid collector of vintage, and mainly British, hi fi gear thinking they would be right up his street. He was a stickler for originality and lack of any modifications etc etc and I was more than a little disappointed when I next visited him a month or so later to find that he'd scrapped these well made and in good nick speakers basically because they were the kit version!
The SFB woofer had a very compliant foam surround. IIRC the foam was not yer usual colour either... maybe white...
It was designed to have a very low resonant frequency as it was used open baffle and, to avoid efficiency and power handling problems, without the crossover boosting bass below resonance.
I had the opportunity to examine a set many years ago but the foam was 1/2 rotted then (about mid 90's ish) and the new owner did not want to risk connecting them up so I never got to actually hear them. IIRC from all that time ago they had a 15" lower bass driver and a 12" upper bass driver.