I think you'll find the chance is a lot less than 1 in 1,000,000.
i) there's a fixed pool of numbers in each area code, which might still be linked to a specific geographic area – depending on how BT do their number management
ii) most don't get released and therefore can't be reallocated to someone else.
If 10,000 numbers got released over the last two 1/2 years, the chance would be down to 1/10000, which is a hundred times more likely than your estimate and it could be a lot lower. Also, a lot of different numbers would seem like an incredible co-incidence for a whole lot of reasons so you might end up with a much much more likely chance of hitting on an 'incredible coincidence' that you might think.
And yes I am stats geek. And I'm married to an even bigger one, who will laugh when she reads my geeky post later 😀