Just got my result through and its 450Bq m3.
Should I be concerned and what can I do to reduce?

According to this link:
http://www.ukradon.org/information/level
action is required. Talk to you local authority environmental health dept/ building control. If you are living in a Radon affected area above the trigger levels, they should be able to give good advice.

FWIW, all that can be done is putting down a Gas barrier membrane that seals the gas beneath the floors and vents it out to one side. Depends how your house is constructed.

Ive installed this before at work. Obviously retrofitting it is more complicated than including it in your build.
http://www.pageo.co.uk/PAG_gas_brochure.pdf

You can also get a spray on version

http://www.pageo.co.uk/gp_housing_membranes.html

Is this based on the Radon risk maps or actual testing?

Is that the result from mapping, or from monitoring? Just had some discussions over a site in Glasgow, and the council have stopped requiring radon protection as the mapping wasn’t matching up to recorded levels. First point of call is the council environmental health officer or contaminated land officer. Then there’s various ways if retro fitting protective measures if needed. The limit for commercial buildings off the top of my head is 400. Whereabouts are you and do you know if your house has a solid concrete floor or suspended (vents close to ground level around the perimeter)?