This carry-on rule is Europe-wide. It is not limited to BA and England. If you check the history of this new system, you will see that it was decided by the European Union in consultation with the airlines and the security people amongst all member states. Every member of the European union is expected to enforce this carry-on baggage regime. Implementation of course will vary over time and place - this is not unusual. But sooner or later all will comply, or the system will be changed.
That's a feature of the British mentality. We routinely enforce (and obey) rules prescribed by the EU which are equally routinely left unenforced by other countries in the group. We seem to take a perverse delight in giving authoritarian powers to small-minded men who (apparently) hate the travelling public and delight in making their lives difficult. It's part of our English charm. Last time I flew to London (internal flight from Manchester), with only hand baggage, my shaving foam was confiscated: no apology, no explanation, just taken and dumped in a bin. Apparently it's a terrorist tool (at least, it has been since last year: it was perfectly safe before then).
The ostensible reason why this is happening is because for the longest time the airlines have been trying to limit carry-on baggage. It is a huge nuissance for them.
That really isn't true. Before the huge scare last summer (I think it was last summer), the no-frills airlines, such as Ryanair, had been desperately trying to discourage checked baggage and encourage hand baggage instead. They had introduced a charge, in addition to the ticket price, for each item of checked baggage: FlyBe, who bought all of BA's non-London European routes earlier this year, still do that (EUR6 in advance, EUR11 at the airport). The reason? Checked baggage needs baggage handlers, ground agents and so on, and slows down aircraft turnround on the ground.
Since then, they may have changed their collective minds, although I think not. The other advantage to the airline in confining passengers to carry-on luggage is that they can fill their holds with cargo, generating more revenue.
Still, if we want dirt-cheap flights, we're going to have to compromise somewhere, and dirt-cheap flights are very much around, at least in Europe. I've just booked three one-way tickets from Limoges to Manchester (a 2-hour flight) for EUR31 each: with taxes and other charges, EUR60 each. I'm not expecting a pleasant journey!