Wouldn't avoid tax any more than any other multiple unless it was combined with some sort of 'x on y back' instruction. There's no option to do them online but I'm sure any office would take it, there's no reason why not. You might have to explain what you mean though as it's not very common. Probably about 5 years since I put one on in my local bookmakers shop, the lady who took the docket showed it to her male colleague (who was presumably more experienced) and he combined a nodding motion with a grunting sound which she seemed to interpret as affirming that he understood the instruction.