Thanks for the photos, I think that helps. My initial reaction is to start again and take this at face value. Start with frame/model identification then look at the frame number. The frame feature are fact, the number is speculation at the end of the day and will have errors and anomalies.
The paint work looks fairly original and the decals are consistent with others in the database from the period. H Lloyd lists these as in use during the 70's and 80's. So can you recognise this as a Triath-Elan? With the history site temporarily down you will have to relay on forums and Google images.
The number is consistent with the post 85 era, although in the correct position it's split. We have other 6 digits numerals starting with 1 in the database, but not with a preceding letter. It could well be this is the first we have seen like this. We do have a number of frames that do not fit the common systems, some are earlier than yours and a bit suspect. The rest are similar and I see no real logic to them. To me the numbers start very high and could signify a clear break with the previous 6D numbers when Marlborough took over, there may also be some significance in the first two digits and the date, who knows. The last three numbers seem to be from the Falcon period and start with B and C Two of these have aero levers which would place then late 80's on wards.
As the 6D system seems very consistent and covered everything made by Holdsworth I am of the opinion your frame is post 85. On face value its a Triath-Elan and if this model finished before 85 for some reason it picked up an odd number. May be there was some early frames that picked up the new numbers, but I am inclined to think this is post 85 and is a variation of the other numbers starting with 1. I am inclined to drop the Trek idea on the basis that you have to explain the H in the number and establish a link with Holdsworth.