I am not familiar with the UK law, but in Portugal any lawyer or solicitor would tell you that they deliberately 'forgot' to word it rightly, wich would be something like this:

Whilst British Airways will make every reasonable effort to provide you with the products listed above, for operational reasons, we may not be able to provide all of them. If we fail to do so, we will compensate you accordingly to the value of the services or products that we didn't provide.

Although companies are not required to explicitly write that you will be compensated if they fail to provide the service that you rightly expect from them, this would be what would be enforced.

OTOH, what do you define as 'reasonable effort'? For me it is not 'reasonable' that this gets going for more than a couple of days.