I do agree with you that planted tanks are kind of a backwater in the UK.
In part the equipment is expensive, but I'm also apalled at the poor quality of the plants normally sold in fish stores.
Just a few months ago I picked up seven Java ferns from a very well respected store. Took them home, unpotted them, and found them to be nothing more than loose leaves, no roots, no rhizomes, just leaves. For want of anything better I simply floated them in the breeding tank and some have produced plantlets. But still, most aquarists wouldn't try this, and figure the inevitable death of the plants means that aquarium plants generally are a waste of money.
There's also the issue of so many standard tanks having lighting units that cannot possibly grow plants, and the majority of the cheaper aquarium plants being once that need lots of light. Put this together, and that's a lot of dead Amazon swords and Hygrophila. And don't even get me started on non-aquatic aquarium plants!
So in my view, until the retailers get their act together about making plants "possible" for the average aquarist, I'm concerned that for most people growing aquarium plants will remain an iffy sort of afterthought rather than something as much fun as, say, breeding fish.
If you do want to write for them, I'd suggest reading
this page at the TFH web site. It gives basic guidelines on writing, and though specific to that magazine pretty well hold true for all of them.
Cheers,
Neale
For me the magazine has a very strong old-school, low-tech bias with regards the planted hobby and I feel some "new blood" may help provide the ideal kick this hobby needs in the UK.