Big thanks to @Pottermus for sourcing me some new genuine brake caliper slider pins. Sadly though upon removal of the old pins I managed to completely sheer off the top of the bolt head, which was a big woops. I then tried to drill a hole in what was left of the pin and use an easy out tool (reverse thread tool) and managed to snap that in the hole as well. Bugger! So currently have the car sat on an axle stand, in gear with the wheels chocked, so it's not going anywhere. Got my sister to give me a lift to the scrap yard tomorrow in the hopes they have a car that I can get one off.