I'm not so sure it's a conspiracy in the sense of "organised, coordinated and covert attempt to achieve something" but there is definitely a community of interest between the banks, retailers, and government in respect of a move to a cashless society. The banks get to save costs, the retailers save costs and online and impulse purchases become easier, and the government saves the cost of producing coins and banknotes as well as finding that all monetary transactions are now traceable for tax purposes.
However, experience has shown that ordinary people can be pretty resourceful when riled. There are already informal local currencies and credit/barter schemes springing up around the UK so that low level transactions stay off grid and untraceable.
In a manner similar to derivative trading, things that only exist in theory will be traded between members of the community: promises, vouchers, credits, pints... and the harder it becomes to get official currency, the more de facto unofficial currency will spring up.