The tailor was impressed, or would have been if it hadn't meant I wasn't going to buy a shirt on the spot. So - I couldn't resist it - I asked why exactly it mattered that this was an Aquascutum rather than, say, a Marks and Sparks?
The answer, it appears, is in the fabric. Of course a shirt's got to be well cut but you'll know that if it's comfortable when you put it on, if the seams appear to be pulling (if so it doesn't fit), and if, like an atrocity I once picked up cheap from a designer range in a supermarket, it was designed for someone whose wrists are level with their knees.
The rest is in the quality of the material. Aquascutum simply has access to better stuff (ie it throws money at it) than the High Street brands.
So when you pay your money to a designer or tailor, that's one of the key differentiators. Bespoke tailoring of course means you can dictate the exact cut, material, collar etc. and if it doesn't fit absolutely perfectly you're welcome to take it back in a bit of a huff.
But if you were wondering about the price you pay for a designer brand then that's one of your pointers. Of course there's a premium to pay for a prestigious label too, which is largely a matter of supply v demand and how much the designer
Personally I thought for £28 I had a bargain.