Lots of things provide nitrogen for your plants, including whole fish, urine (I do not recommend this), fresh grass clippings; but you do not want to necessarily use them in all situations. You'll get better answers if you're more specific.
What medium are you using?
What nutrients do you use?
What is your pH?
Have any pictures of the problem you could post?
There are alternatives to grow stores, I'm betting, in GB. Does your local home improvement store carry landscaping items? Not familiar with England, but we all have to be creative sometimes... Good luck!
Maybe he needs to let the pH come up a little bit in that range there. The pH range I use is 5.8-6.2. Also, maybe the particular strain he's growing is a nitrogen hog. Or, could there be too much P in his mix, thus leading to lower leaves browning on the edges, yellowing, then dying off?
Wambam, you've gotta give us a little bit more to be certain, but here's a cheap and easy answer for you below that I use on a regular basis. Can't be drinking a buncha beer or iced tea if you want to do it, though.
Yes. Pee. Diluted properly it's a good push. Assuming it's not very watered down from drinking too much of anything, I'm talking a nice, healthy, clear but distinctly yellow pee.
1C/5gals, and if you think it's very strong, use less.
foco ur right mate, i have spider mites,good job its only 4 weeks into veg,i will buy the right products and get rid of them,will it be the spider mites that are yellowing my plants,they seem to be yellowing from the outside to the inside of my leaves.