Simply to clarify the 'deadline', in terms of their use
other than in ticket machines:
Old one pound coins are still 'legal tender' until 15 October 2017;
After that date, shops
may refuse them. However, most banks and Post Office counters will continue to accept them, so you will still be able to pay the old one pound coins into your account, for example.
And, in the interests of recycling,
old one pound coins will be be melted down to make
new ones. When they've removed the metal content of the 'one in forty' or even 'one in thirty' dodgy ones, obviously.