The UltraStudio Mini Recorder is an ultra small pocket sized Thunderbolt powered recording from SDI and HDMI - blackmagicdesign.com 
The UltraStudio Mini Recorder is an ultra small pocket sized Thunderbolt powered recording from SDI and HDMI - blackmagicdesign.com
It costs around £130 from amazon.com It's worth checking it works before purchasing it though - so I'll try the shop rather than order ti online?
London based shops where you can go in and get advice include:
130 UltraStudio Mini Recorder
This device is required in order to convert HDMI signals from a camera into something that the computer understands. HDMI ports on laptops are for output not input.
Based on previous experience, these devices can be a bit fiddly to get working - you need the right settings.