The British 240V mains is nominally 230V rms
Vpk = sqrt2 x 230V = 325V
Vav = 2/pi x 325V = 207V
If you look at your AVO8 you will see that 207V on the dc scale (which is what it is measuring) corresponds with 230V on the ac scale (fudged to indicate rms but only for sinewaves). The fudge factor 1.11 has been used when making the ac scale.