Never tried M&S myself - might give it a look next time I'm in the market for a whistle as I'm an odd shape and find it hard to find clothes of any description that fit well (stumpy legs and arms and a long torso). I have, however, bought a bespoke suit from Savile Row (long-held ambition made possible by a generous bequest in the will of a distant relative) and I have to say that I have never bought off the peg since. It is the nuts - not least because you get to do that whole half-finished, chalk-striped and pinned first fitting thing. You also get treated like a Lord and feel great that you are buying something hand crafted and of impeccable quality. You can do things like take it back for running repairs - there is a whole after-sale service thing you just don't get with off-the-peg. What is more, you find that you carry yourself differently when wearing it - a bit more authoritative. I've since bought whistles, trousers and shirts from a tailor in Singapore, but they are very much Div.2 in comparison to the Savile Row number (it's getting the cut and fit of the jacket right that seems to sort the men from the boys). In summary, I'd say do it if you have a couple of grand kicking around to spunk on threads - it's worth every penny. P.S. No they don't ask you which side you "dress". Hughesy.
 

Bloke I met who bought a full on Savile Row whistle in extremely similar circumstances was heard to remark, "First time I put it on in front of the mirror I got wood, I sh1t you not.". Of course it wasn't Bill Goss who's been known to achieve the same effect for a far more meagre couple of grand CZK.
 

That always happens when I look at myself in the mirror...! Hughesy