Britain has... err... 7.7mm Browning or Vickers
Plus 20mm Oerlikon FF type cannon (not sure what mark but lets say its based on the FF with drum feed and built under licence, call it FFB or something?)
I'm sure Vickers could make a 12.7mm MG or even a 0.661in HMG for aircraft use if anyone wanted it.
Nothing earth-shaking but the rip of eight 7.7mm sounds good anyway...