In 2006, only two hundred out of ten thousand trainee primary teachers had technical, numerate (STEM) degrees, and this number was half the figure from 2004. It is clear that teacher subject knowledge is a key factor in the success of pupils (e.g. here), but it is also plain that specialists are very rare: out over a hundred Initial Teacher Training courses, nearly half offer an emphasis on a modern foreign language, one offers mathematics and none science.
The Williams Review into primary school Maths teaching recommended in 2008 that much of the current malaise in maths education could be solved if every primary school had at least one teacher with a 'deep understanding' of mathematics, so we ought be pleased that the government has announced a program to provide maths 'specialists'.
But, as with many government solutions, the Maths Specialist Teachers Programme (MaST) is more about appearances than solving the shortage of expertise. In service teachers are to be given three autumn-term days of training at a university, two weekend residential and twelve half-days of in-school support over two years, after which they will be described as Maths Specialist teachers.
I don't know how long it would take to turn a primary school teacher, with perhaps a Fine Arts or English Literature degree, into an expert Maths teacher, but I'm sure it's more than the ten days offered in the MaST program.