The Advertising Standards Authority is the body in the UK that regulates advertising, and is backstopped legally by Trading Standards.
In both the "CAP" code that covers non-broadcast media (leaflets, print adverts, signage etc) and the "BCAP" code that covers broadcast media such as radio, TV etc there is in section 3 "Misleading Advertising" the following (emphasis mine):
Marketing communications must not falsely claim that the marketer is about to cease trading or move premises. They must not falsely state that a product, or the terms on which it is offered, will be available only for a very limited time to deprive consumers of the time or opportunity to make an informed choice.
And the "Consumer Protection from Unfair Trading Regulations" have this to say under the list headed "The following practices are banned outright":
6. Limited time only
Falsely stating that a product will only be available for a very limited time, or that it will only be available on particular terms for a very limited time, in order to elicit an immediate decision and deprive consumers of sufficient opportunity or time to make an informed choice.
Both of which would seem to apply here. Of course where Bob has purchased I expect any liability the seller would have would be likely limited to the cost of the product/service. Where Bob hasn't purchased anything? Bob could of course bring the misleading advertising to the attention of the ASA who may act regardless, they don't care whether Bob has purchased anything or not, of course Bob probably wouldn't get any compensation or the like because they have no damages.