Anyone that does anything more that 5 minutes trail clearance will know that secateurs are useless. You don’t get anywhere near enough done in a reasonable time.
You can acheive a reasonable amount of whacking/ slicing with a folding saw, and it can actually reasonably sized logs and branches too. I’d start here with something that has an 8″ blade.
Taking it up a notch for brambles and such benefits from the use of a brash axe or machete. Personally, I find a machete way more effective that a brash axe, but the potential to injure oneself is higher with a machete, and I’ve been informed by a friendly PCSO I know that if seen by plod, I may be liable to summary arrest, with questions asked later. I’ve never seen plod away from Tarmac though.
For bulk work, I have a portable electric hedge cutter.