Southport/Birkdale Sands (EGCO) is AT sea level - its on the beach!! Although not sure if its still operated anymore.
Don't know of one below sea level.
Good posts. Can I ask for more info on who you were getting radio services from on your travels.
Not been "dahn sarf" yet, and it might prove helpful once my lottert ticket comes in, and I get the chance to follow in your foot steps. :-)
Keep up the good work.
RH