Almost certainly would be Northeast Airways, one of the short lived amalgamations in the late 60's/early 70's and Newcastle based, if memory serves. I remember returning from Bilbao to Gatwick on a Northeast Brit in 1971, I think.
That depends on the date.
BKS Air Transport, formed in October 1951, initiated Britannia services from Newcastle to Heathrow and vv in April 1964. The Britannias were progressively withdrawn from the route from December 1968 and from April 1969 Tridents took over.
At the end of January 1970, BKS had just one Britannia left, G-ANBK, which was in store as a standby aircraft.
BKS had become part of the British Air Services Group with Cambrian in March 1967. This was not an amalgamation, it was a legal entity formed by BEA to look after its stakes in BKS (50%) and Cambrian (33%) and to investigate the operation of short sector services within the UK using Short Skyliners. Saunders ST-27s and DHC Twin Otters were also demonstrated to the management, and the Skyliner was used to conduct a tour of airfields selected for the proposed routes.
This was the only flying activity undertaken by BAS as an entity - the idea was not proceeded with for a variety of financial, operational and regulatory reasons.
Cambrian and BKS continued as independent trading and operating companies both carrying British Air Services titles as "sub titles" - the BKS Tridents carrying the titles on the cabin roof with BKS tail logos, as did some Britannias and Viscounts. The rest of the fleet carried BKS on the cabin roof and small British Air Services titles near the passenger doors.
On November 1 1970 BKS changed its name to Northeast Airlines, to emphasise its links to North East England. It adopted the same yellow colours as Northeast Airlines in the USA but in a different layout. The renaming was simply that, no merger or amalgamation was involved and the opportunity was taken to relegate the British Air Services titles to the nose. Cambrian adopted a similar colour scheme layout (their BAS titles had always been much smaller) using a poppy red colour.
In December 1970, G-ANBK was overhauled, painted in Northeast colours and operated a number of fill in services, including Newcastle - to London, for a variety of reasons during 1971.
On December 31 1971 it flew NS442 from Newcastle to London and was then withdrawn and scrapped. NS442 was the last Britannia 102 flight ever.
In July 1973 British Air Services, as part of the former BEA, but itself until then not absorbed by British Airways, became part of British Airways and financial and legal arrangements were made so that Northeast as a whole came under the control of the British Airways board. The aircraft started to appear in BA colours but carried Northeast titles and used the Northeast callsign until March 32 1976 when the airline became part of British Airways Regional Division - following Cambrian which had been taken out of BAS and absorbed by the Regional Division in September 1972, immediately losing its titles on the aircraft and, by 1974 having no separate identity.