Hello,
Here's how it works:
You don't need planning permission, but the beam that you use will need to comply with the Building Regulations and must be inspected. You can submit plans if you like, but it more usual to fill out a Building Notice and then get it inspected from that. The point is this, that if you submit plans and details, and then do it as stated, then you won't have any problems with the installation, whereas with a notice you'll get it inspected AFTER you've put the beam up. So you'd better be sure you've done it right!
Depending on what type of beam you use, you may be asked for calcs, to prove that it's up to the job. However with a catnic you can get the calcs from the manufacturer, because they are deemed to satisfy. Otherwise you'll need someone to do the calcs for you.
A quick rule of thumb: opening width/18 = beam height.
You should also set the beam(s) on concrete padstones if you're using RSJs
Tony.