Decca had a Jetstream, Bell 47 and a Prince at Biggin - probably part exec transport and part systems development?
Taylor Woodrow had a Twin Otter for some reason.
Tarmac had a Agusta 109
One of the brewers used to keep a PA-31 at Biggin - might have been Bass as mentioned above.

Then there was the 'Robertsons Jam' owned Navajo registered G-OLLY.

Scottish &Newcastle Brewery had a citation at EDI G-OSNB and kwik-fit had a king air I think, EDI based too.

Marconi had two jets at its peak - one which flew every day to its Italian base in Genoa as the commercial routes took a day to get there given the schedules. No idea what type it was, but it seated about 12 and it flew from Coventry airport.

The second one did the Pittsburgh run, and was bought when BA stopped flying to Pittsburgh direct, and the change was a bit of a pain. In good old 'lack of planning' organisation, it turned out that international private jets werent allowed direct into Pittsburgh, so the private jet had to stop at Newark for immigration. I am not 100% sure but the jet was fitted out with large business class style seats only and the story was that they got a good deal on the aircraft as it was destined for Arnold Schwarzenegger, but he cancelled at short notice and Marconi snapped it up cheap. Marconi went bust about a year or so later.

Weren't Vernair also a charter company rather than just being private ops?

Also Hawker Siddeley had a fleet of Dove's

Fox's Glacier Mints ran a Rapide (G-AIDL) out of Leicester for many years in the 50s/60s, alongside the English Electric Heron flown by Alan Firmin. Alan had his own Decca approach to cope with the inadequacies of Leicester East ! The Heron had a regular schedule to Valley to cover the construction of an early nuclear power station on Anglesey. (Wyddfa ?)
I also remember first a Beagle 206 then an Aztec, owned by Associated Tobaccos which operated for a few years until it was, I think, written off during an asymmetric refresher.
A long time ago so could be slightly wrong on a couple of aspects.

Fairey's used a Bristol Frightener to move stuff to and from Brussels

British Car Auctions
Iceland Frozen Foods

Operates an A109 from Fairoaks.(G-FRZN)

Wasn't there a Heron operated by British Nuclear Fuels or some such organisation?

Marconi had a Piaggio P.166 for quite a while, remember seeing it over South Croydon one day many years ago - now in the Science Museum collection at Wroughton.

Another corporate twin once seen beating up Purley's "Volkswagen Building" just a stone's throw from where I type this was VW's Islander - used for parts distribution I think!

Just as a sideline, you can still fly in the Dragon Rapide G-AIDL, mentioned in post*26 by Sleeve Wing. It is operated by Classic Wings at Duxford..

Lego Citation at Fairoaks in the 80's as in Lego had a Citation, not an actual Lego Citation :)

Whitbread had a Navajo G-BREW

Ah yes, that was the one that lived at Biggin...

'IDL operated joyrides from Biggin in the 1970s and '80s as Southern Joyrides, owned by the late Mike Hood. Nice guy, had a lovely flight over London in the old bird.

I believe Birds Eye Foods had a Queen Air (based Fairoaks?) in the '70s.

De Beers used a Do 228 for transporting diamonds at Fairoaks in the '90s but don't tell anyone.

Operated out of Farnborough later; larger Citation (650 I think) whilst they were building Legoland at Winsdsor.
IBM used 3 different Falcons at Farnborough in the '90s too.

I operated G-BREW out of Biggin for many years. Great bunch of guys to work with and the aircraft flew its socks off just as a good corporate should. Real shame what eventually happened to the flight department but thats what comes of listening to "experts".

Out of Leeds / Bradford Asda used to have a corporate jet when they were owned by Walmart as a friends wife was their marketing director but not sure of type.

I worked for Saint Gobain and back in the 90,s for a while, and there seemed to be an airforce available to our French opposite numbers, sadly not allowed on them if UK based it seemed.

Cheers
Mr Mac

A construction earthworks company called Cinnamond kept a jet ranger at Luton. It was G-DOFY (Duchess of York) and was the one Fergie bought to learn to fly in.

It was rumoured to be mostly used for the owner to go to French vineyards to buy his wine at source.