It looks similar to a No.20 or 21, but the base looks wrong to me - almost as though it was intended for a plinth. I think both these bowls have a conventional foot, but dimensions would help here as it is recorded at 9-in (23cm) diameter. A little variation is known, but only ΒΌ-in (6.5mm). I do have a No.20 that I can photo for comparison, if required.