I have sent few emails and soon I got a response from Gavin Dixon working there. It read
"Given the research you have already done on the instrument, I don’t think there is going to be much in our archives that will be of help. [...] records of instrument production at Hawkes & Son are very poorly represented in the B&H Archive. When the two companies merged in 1930, Boosey & Co was by far the more dominant force. It was Boosey serial number sequences that were continued and Boosey archives that were retained."
And he has attached a detailed hand-list of the archive which now is also available online. Unfortunately it proves his point very well. Out of all the documents there are only two that could be of interest to me. First one is a journal [(E82.36) A227/138] with woodwind production by serial number with numbers from 7664 to 15631 produced between 5 March 1921 and 17 February 1931. The second one is a plating book [(E82.38) A227/141] listing instruments sent for electroplating between June 1928 and December 1931.
Later he added
Later he added
"I have heard though from many sources that by the 1920s, Hawkes instruments, and woodwind instruments in particular, were clearly superior to those being made by Boosey. [...] I don’t think the 13 on your instrument is a serial number. It is more likely to be a model number. I would imagine that your bassoon is probably of cocuswood. It is probably also in high pitch (ie a=452.5 hz)"
and also in another email
"In terms of the serial numbering, it may be the case that they had a number sequence for instruments they made themselves, while other instruments (such as yours perhaps) were made by another company and sold by Hawkes. I think that Morton made oboes for Hawkes in the last years of the 19th century that were sold under the Hawkes name. Just a thought."On their website I have found the first picture of a bassoon looking somehow alike mine but the information to complement it was very sapre. 'Bassoon. Cocuswood body. German silver mounts. 15 German silver keys. French system. Rollered F/G-sharp key, three keys on wing joint for left hand thumb. Key guard embossed with an H. Crook with vent hole.' I have studied the hand-list just to find out that there is nothing really helpful. Theoretically the Journal could be but it looks like Hawks & Son kept their serial numbers in strict order so it is very unlikely I will find anything about number 13 between 7664 and 15631. Or even worse if Gavin is right and the 13 isn't the serial number at all then there is no reference point at all.
I have also found A GUIDE TO DATING BOOSEY & Co./BOOSEY & HAWKES INSTRUMENTS BASED ON SERIAL NUMBER on the Horniman website but again it is mostly about Boosey not Hawkes and there is no trace of two digit serial numbers there either.
To be honest I hoped to find there something more specific about the construction of the instruments and the techniques used that could help establish something. The hopes were high but now it looks like I'm back to square one. No questions have been answered.