I dont think it will be a problem.

I would imagine the reason no float is stipulated - and it is certainly prohibited in the EA Midlands byelaws, is that it would make it exceptionally difficult to police who was, and was not complying with the rules in the close season. Anyone using a float, correct gape of hook, and worm section could fish all day with impunity regardless of their target species.

If someone is using a fly rod, and has a fly on the end on a river that has trout in it, i think indicator or not you are ok!

__________________
Around the steel no tortur'd worm shall twine,
No blood of living insect stain my line;
Let me, less cruel, cast feather'd hook,
With pliant rod athwart the pebbled brook,
Silent along the mazy margin stray,
And with fur-wrought fly delude the prey