You can go to the Boots or Superdrug online pharmacy, do some basic questionnaire, and then it need signed off by a pharmacist, and a day or two later you an collect it. Easy. And I'm not shy picking it up. It was worse trying to buy top-shelf magazines at 16.
Sidenfall is the generic of Viagra so will be cheaper. And sometimes they give you the Viagra packet even if you order Sidenfall. Yes, you need stimulation for it to work, but you should notice a difference. Personally, I use occasionally, as it doesn't seem a good idea to me to always rely on pharmaceuticals.
Some other good ways to boost the little man's performance:
1) Critically, get enough sleep.
2) Less critical but obv abstention from blowing your wad (as in hold off for a day or three, not never enjoy fantasy channel or whatever)
3) Go do some weights, especially the compound moves like barbell squats or dead lifts.
4) Lose weight if your carrying a few extra kilos
5) Avoid soya foods, like soya milk, tofu etc