> It's also good to remember how much breakfast regularly costs now. £15-20 is quite common at mid range places - £10 of yesteryear is exceedingly rare

There exist hotels where breakfast is still very cheap (but the rooms are accordingly more expensive). The reason is that business travelers, the budgets for meals are really tight (you have to pay anything above by yourself), but the maximum allowed costs for hotel rooms are typically much less tight.

To accommodate such business travelers (though these are not the only guests), the hotel makes the breakfast really cheap, but the room accordingly more expensive (but still within the typical budget of business travelers), so that such customers can deduct more travel expenses to the employer.