As Conanius said, do a course you are interesting in NOT what you think might be wanted by employee's, the most impressive thing about an OU degree, or a decent degree is that you do it rather than what it is. Then depending on the difficulty that also says a lot, being able to finish a full on maths degree shows a level of thinking and intelligence that many other subjects don't, and maths will take you to a ridiculous number of places, largely because great maths foundation makes getting into computing easy(maths is hard, programming is fairly easy) and just about every industry has computers doing something critical these days.
If you do intend to do an OU degree, sign up for a module, ANY module RIGHT NOW. If you sign up and start a module for this jan/feb, on the current pricing and continue onwards, then you will continue paying CURRENT pricing, IE £400-500 a module, if you sign up next october, you'll be paying circa £1000 a module and £4-5k a year. So it makes a heck of a lot of financial sense to jump on board asap. You can even just do one, or two modules for a fairly lightweight year and a good chance to get back into learning and without as much stress and time needed.