It was pointed out by Gregory.Rotter on cameralabs.com that this camera/lens combination was front focusing. Now because I’m a newbie with an untrained eye I hadn’t noticed this. After a bit of google action I came across a test sheet, downloaded it and ran the test
Here’s the result
Model: Canon EOS 550D
ISO: 100
Exposure: 1/250 sec
Aperture: 1.4
Focal Length: 30mm
Clearly front focusing 
And I’m loving this lens
So after another bit of google action I found there was a Sigma Service Centre in Dubai HERE. I gave them a bell and made the journey there to drop the lens off. It will be with them for 14 days 
I have taken another test with my Canon 50mm f1.8 to check its not the camera. I’ll upload it and post it shortly
Ian Ganderton 
i have this lens if you are havin bac or front focusin ust use the live view mode and its gone on my d7000 camera i can go in to its autofocus menu and calibrate the camera to the lens to Perfect focus BELIVE ME ORE NOT its not the lens thats the broblem but the camera is not calibrated to Your 30mm 1.4 lens its the camera thats is selecting the wrong mine is 100% Perfect in focus after calibrate and the camera is recognizing the lens every time
I have the same, in live view the focus is fine. It’s to do with the different way the camera focuses in the different modes.
The 550D doesn’t have the option to calibrate the lens in the same way the 7D does.