There is a huge amount of UK infra now that is dependant on US companies either directly or indirectly (AWS, Microsoft/Azure). Code, data and infra is locked into US platforms. When US-EAST-1 when down last week, it halted our whole operations at our workplace. Looking at freelancer groups I am part of (whatsapp, slack etc), they had the same experience.

The UK being blocked from the outside won't happen anyway. The large tech giants will just either cut a deal (this already happen with Apple/iCloud), or they will comply with the new acts. The sites that don't comply won't be big enough for anyone to care in normie land and thus there will be no real pressure on the UK gov.