A bonus cache for the Wheatley AdLab. You'll need to complete that to get the required information to find this.
The coordinates will bring you to another lost pub, The Crown Inn. There are two signs, one on either side of its arch.
The number on the left minus the number of letters on the right minus 1 = D
To get the final bit of information that you need, you'll need to visit stage 2.
The cache is at N 51 44.ABC W 1 D.EFG