These are what I buy for myself and others most of the time:
http://svp.co.uk/product/verbatim_silver_top_16x_dvd_r_(43550)_3798_box
These are all excellent choices too:
http://svp.co.uk/product/verbatim_dvd_minus_r_16x_silver_top_(43548)_3398_b ox
http://svp.co.uk/product/verbatim_16x_dvd_minus_r_(taiyo_yuden)_(43548)_365 2_box
http://svp.co.uk/product/verbatim_branded_16x_dvd_r_(43548)_3787_box
Price are PRETTY MUCH IDENTICAL to what it costs in the USA or Canada. It's about $15-18 for a 50-pack, or $70 for a 200-pack. To spend any less money will get you crappy discs from CMC, fakes, RITEK, etc. With cheaper media, all you save is maybe $5, but you end up with tons of coasters and discs that must be replaced. Verbatim tends to burn 100% perfect all the time.
For your £20, you can pick up 2x 50-packs, so 100 discs. That's a good price. And those are archival-grade discs.
Use them for special needs, your own masters of sets, etc. Keep the cheap ones for people you don't like, freebies