Distance from washbasin to soilstack

[simpsonstu]

Trying to put an understairs bathroom in and a plumber has told me the max distance from washbasin to soilstack is 1,7m.The closest distance is actually 3m.Looking at the building regs it says you can go to 3m with a 40mm Diameter?,Is this correct or is my only option a saniflow?
Help appreciated,thanks,Stu