Hi and

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I think the frame could be made from Truwell, similar material but electrically seam welded. If you remove the seat post and look down inside for a seam running the length of the tube you will be able to tell. If it doesn't have a seam it could possibly be 531.
I have a Black Diamond , it might be the same year as yours but it doesn't have chrome forks and it is deep flamboyant red. It does have the same Simplex rear derailleur though . Does yours have chrome wheels ? I have fitted alluminium ones on mine and it rides a lot better now .
It is one of my favourite bikes to ride .
I'll have a look for the thread about vintage Falcon cycles and try and find the bit with a catalogue in . The search thing isn't very helpful !