I would agree that was the most likely option.
GOR.339 says:
Most WW2 airfields, in the UK at least, had 4,000ft long runways at least, most RAF stations had 1x 6,000ft and 2x 4,000ft runways - so did some 8th AF fields. So in theory, assuming the runways were mostly intact, there should have been ample length with some to spare.
[URL unfurl="true"]https://masterbombercraig.wordpress.com/avro-lancaster-bomber/ground-crew/raf-station-runways/[/URL]
But it does go onto say "unconventional means" which ended up with the Shorts VTOL piggyback-style solutions and it does it say "If runways are used operation is to be practical..." - my bolding for emphasis. So non-runway (probably PSP or compacted dirt strips) were considered likely when the OR was thought up in 1957.
OR.343 says:
An LCN of 20 would the same at the Avro 748 or a C160 Transall (at just over gross weight) (the Argosy's LCN was 33)
There is an interesting discussion on LCN numbers and what that mean for WW2-era infrastructure. An aggregate soft surface strip from WW2 would be about LCN 15. Improving that to LCN 25 when dry would require excavation and hard core underpinning.
[URL unfurl="true"]https://calclassic.proboards.com/thread/5523/soft-runways[/URL]
Paved runways and taxiways from WW2 would equate to LCN 50 and most commercial airfields were upgraded to LCN 65 in the 1950s. The Short Belfast was qualified to operate at LCN 65 at MTOW.
So it seems unlikely that TSR.2 could not have used existing airfield infrastructure in the UK/Western Europe. Overseas would be a different matter of course - but any Allied-built airfield should broadly have conformed to those LCN limits.
It does seem that airfields are preferred but the distances quoted here leave a lot of margins on most airfields for safety, the engine-out condition could require 7,000ft to land with zero flap - as much as 9,000ft in the wet.
The following were the basic parameters for operational use:
Normal peacetime bases: minimum 8,000ft with permanent arrester installation
Exercise bases: minimum 6,000ft with portable arrester gear
Operational use: minimum 2,400ft
The specs also wanted serviceability with minimal work for 30 days stored outdoors without cover, not entirely practical and Handley Page came up with a large servicing tent.
It looks like the more basic requirements for ground support kit were deleted.
Likewise so was the SRV (Servicing and Readiness Vehicle) in favour of a cheaper Bedford-truck based TTRV (Turn-Round and Readiness Vehicle), but no work on that was started either. A large ATE (Automatic Test Equipment) vehicle/trolley was also required.
