Mrs. ND76 and I used the Number 1 lounge yesterday flying C+ on a V fare bucket LHR-PHL. The signage for this lounge clearly mentions Delta Gold Medallion as eligible to use this club.
The one glitch about this place was the cumbersome nature of being admitted (those without status can enter by paying GBP45). The concierge at the front counter needed to make photocopies of our boarding passes in order for her company to get paid by Delta. She had trouble operating a small photocopier; it took close to 10 minutes to be allowed into the lounge as a result.
There were a few self serve refrigerators around the club dispensing soft drinks and still/sparkling water bottles. Adult beverages were served at the bar. Beer was served in half-pint glasses. Complimentary hot food orders were taken at the bar and served at your seat by waitresses; I had a very tasty bacon roll; a couple near us ordered a pasta dish and a hamburger, and both places looked very good.
There were showers and a day spa available.
It wasn't the Clubhouse, but it was serviceable.