Saben, Hart & Partners are tough to track but they did a minor connection with the Saunders Roe Princess. Indeed Saben, Hart seems to have had a minor finger in lots of bigger pies -- aviation, nuclear power, architecture, etc. BTW, a Raymond Hart is mentioned as a director of Saben, Hart & Partners in a 17 Nov 1957 article in the
Sydney Morning Herald.
https://www.newspapers.com/newspage/123531388/
And then there's this snippet:
"... to join a firm of consulting engineers, Saben Hart and Partners in 1951 as a Senior Draughtsman. The company had a contract with Saunders Roe and my first job found me working on their SR 53 fighter and Princess flying boat, both were later cancelled. I was then transferred to work on the new Aden aircraft gun. I had enjoyed the work and was disappointed when the company closed in 1954, due to lack of orders, leaving me unemployed."
Alan Mann,
Some of my Teenage Memories, pp.14-15
http://www.memoriesofwar.org.uk/documents/Some_of_my_teenage_memories.pdf
Since P.W. Parish, AFRAeS, joined the Saben, Hart aircraft division in Bournemouth in mid-1956, this part of the firm seems to have popped in an out of existence until 1958.
https://www.flightglobal.com/FlightPDFArchive/1956/1956%20-%200543.PDF
The London Gazette, 23 Sept 1958, pg.5852
SABEN HART AND PARTNERS (RESEARCH & DEVELOPMENT) LIMITED (Creditors' Voluntary Winding-up) [19 Sept 1958]
--
https://www.thegazette.co.uk/London/issue/41505/page/5852/data.pdf
Despite all that, Saben, Hart & Partners Ltd. in mentioned in
Hansard (10 Dec 1962) as contractors to the Ministry of Supply and the Ministry of Aviation.
FWIW, a few divisions listed in The London Gazette, 30 Sept 1960:
Saben, Hart & Partners (Bournemouth) Limited
Saben, Hant & Partners (Bristol) Limited
Saben, Hart & Partners (Coventry) Limited
Saben, Hart & Partners (Glasgow) Limited
Saben, Hart & Partners (Portsmouth) Limited