Alan sent me an IM just before he started the thread. I have been in touch with Alan off-thread to let him know that I should be able to dig out quite a lot of information as Lambournes belonged to my husband's family.
The following is from memory, so shouldn't be taken as entirely accurate at this stage, but I will sort out the details in the next few days and add them here, as well as sending them to Alan.
The ancestry of the company that became Lambournes in Great Hampton Street is complicated and had its roots in the filemakers (Heptinstall & Lawledge) of Ann Street and later Granville Street (see other threads on the forum, though I haven't yet reposted the pictures). Thomas Barret Lambourne married Eliza Heptinstall (daughter of the filemaker in Granville Street) and after Mr Heptinstall's death, Thomas B Lambourne ran a business in the building in Granville Street. Thomas and Eliza had six children (three sons and three daughters). The three sons went into the family business, which then took several different forms over the years from the early 1900s. I think that at various times it was owned by his grandfather + great uncles and later just his great-uncles, when his grandfather started a different business. Lambournes stayed in family ownership.
I'm certain I have some good pictures of the three sons and some newspaper cuttings from the the early 1900s and also the 1930s. In addition, I think I may have some further background information, but I need to have a search through my 'treasure' trunk. The history of the company is difficult to explain concisely as there was at least one dissolution of partnership and re-forming of a different partnership. I need to have an in depth chat with my husband so that I get the information correct!
