Brake fluid coming out of pistons  

oh these are shimano brakes

Sounds like the pistons have popped out or have came out too far.  Pushing back the pistons on Shimano brakes require you to use a plastic tyre lever or something similar as the pistons have ceramic tops which can crack easily if forced back by a screwdriver.

Take the pads off and gently push back both pistons until they are fully home, fit spacer and rebleed.  

I've tried pushing the pistons back in with a brake lever but they are not moving back. Should I open the bleed port on the lever and then try push them back in?

Yes, that should allow the pistons to move freely but you may well need to re bleed the system afterwards.

Managed to get the pistons back in by opening the bleed port on the lever. Unfortunately after re bleeding the same problem persists. Every time I press the lever (with the bleed block still in) the fluid drips out of the left piston, I can also hear a slight grinding noise.  I'm thinking that dirt might have got in to the seal and wrecked it............ 😥 

Looks like the seals have gone or the piston has a crack in it. No option but to buy a full calliper for it as it's a faff changing them and the seals for Shimano. I have two spare XT calipers at home that leak oil because the pistons were pushed back at an angle buggering the seals. 

Even better, buy a new brake kit. 

Confirmation of a broken piston.

Took the bleed screw out and this bit of plastic fell out. Do you think this fault will be covered under warranty? The brake is less than 2 years old.

Hi. Nope it will not be covered under warranty I'm afraid.  New Calliper time as its easier to get this than seals or pistons. 

New caliper should be with me tomorrow 👍  Thanks for your help.