Richard Bridge asked: where I might enjoy an evening sing near Brighton?

Not at all embarrassed to say that my club, Brighton Acoustic Session is on the first Monday of the month at The Prince Albert, Trafalgar Street, BN1 4ED (50 metres from Brighton Station)

The indefatigable Ian Fyvie runs three weekly sessions in Brighton:

    Sundays: The Mitre, Baker Street, BN1 4JN
    Tuesdays: The Round Georges, Sutherland Rd, BN2 0EQ
    Wednesdays: The Pond, Gloucester Road, BN1 4AQ

There is also Mandy Murray's Irish session every Monday:
    The Foundry, Foundry Street, Brighton BN1 4AT

In nearby Lewes - 11 minutes from Brighton by train - you have:

    Every Thursday Folk at the Oak: The Royal Oak, Station Street, BN7 2DA (Until its closure on December 19th, 2013)   

    Lewes Saturday Club The Elephant & Castle, White Hill, Lewes BN7 2DJ

In the surrounding area there is more information here: Folk Music in Sussex