Merchant Navy Use of RN 5A Battledress

[Warspite]

I thought this might be of interest to some. I picked up this rather nice grouping to an engineer in the Merchant Navy on Tuesday:

There are four pairs of shorts, a high collard tunic and most interestingly a private puchase RN 5A working dress uniform with merchant navy rank insignia:

The buttons are RN, kings crown:

And there is a tailor's label for Austin Reed:

What are peoples thoughts on this, is it wartime and the tailors just didn't have the correct buttons? Or has he got the uniform second hand post war and just added his MN rank? Either way its a nice grouping for £40 and the seller has promised me a name and photo of the chap for next week.