Black Diamond
Do you mean Nettleham, just North of Lincoln ?

If so there are quite a few choices.

Market Rasen Folk Club Concert style - Held at Faldingworth Village hall
Mainly every other Friday and Concerts on Saturdays


Lincoln Folk Club Nettleham Same Friday as Market Rasen Folk Club. They are a singaround folk club

Lincoln Folk festival Club Held on a Sunday Night - Concert style - held at the Turks head, Newport Lincoln


Slightly further afield
Gainsborough Folk Club Singaround - Every other Friday - opposite fridays to Market Rasen Folk Club & Lincoln Folk Club

LOUTH FOLK CLUB (singers & musicians nights + occasional guests ~ 2nd & 4th Tuesdays) - YE OLDE WHYTE SWANNE INN, LOUTH

I hope that is of help, if its the right Nettleham :-)