Circuit to switch the polarity of an electromagnet at 50Hz

I have a small electromagnet whose polarity needs to be switched at 50Hz (using a 555 timer?), the DC current to the electromagnet is a 12 volt battery.

My knowledge of electronics is very basic, I have not done anything in this field for at least 35 years!!! So please go gently on me. Even better, if someone in the UK fancies putting this together for me at a sensible cost then I will be forever grateful!

A 555 running in astable-multivibrator mode could do it; there are calculators on the net for the values needed to get that frequency. The output could drive a suitable transistor or a mosfet to power the electromagnet (and you would need a snubbing diode across the coil, of course).

If you need the voltage to be reversed at a 50Hz rate, then the 555 will need to drive a four transistor bridge circuit with a diode snubber across each transistor.

How much current does the coil require?

As you are in the UK, why not just drive it from the mains which is 50hz?
Don't forget to use a suitable transformer to give a suitable low voltage (12v) for the electromagnet.

JimB