White walls are the worst, there will be the most reflections just as that facebook video above illustrates.
A very general ratio is 10-12" in diagonal for every foot in distance.
300cm = 9.84'
So that would result in between 98.4 and 118.08". Generally speaking. Project fist then decide.
A projector like Benq W1110/W1120/W2000/W2000+/W1090 would do, or any other 1080p DLP projector with a RGBRGB color wheel.
Find screen size and throw distance for the BenQ W1110 projector.
www.projectorcentral.com
Or an Epson TW6700.
Find screen size and throw distance for the Epson Europe EH-TW6700 projector.
www.projectorcentral.com
As for a screen, these ones should be fine, but maybe others who are more familiar with the UK's screen market can comment:
Shop Elite Screens SB120WH2 120-Inch 3D 4K/8K UHD Fixed Frame Home Theatre Projector Screen Kit - CineWhite. Free delivery and returns on eligible orders.
www.amazon.co.uk
Free delivery and returns on eligible orders. Buy Duronic Projector Screen FFPS120/169 | 120-Inch Fixed Frame Projection Screen | Wall Mountable | +1 Gain | HD High Definition Image | 16:9 Ratio | Ideal for Home Theatre, Classroom, Office… at Amazon UK.
www.amazon.co.uk
QualGear QG-PS-FF6-169-120-W is a 120-inch 16:9 HDTV 6cm fixed frame projector screen that features high quality ultra white soft PVC fabric 1.2 gain with
www.qualgear.com