If the bridge has been machined off, yes in a sense it removes one of the structural "ribs" across the top of the action. Is it something to worry about? Probably not as much as you are thinking. My book on the No.4 and No.5 family say the charger guide is machined as part of the receiver. Some No.4s have a separate guide that attaches with two vertical screws. (If the designers were really worried about strength, would they have trusted pass/fail strength to two little screws?)
Don't show that to an EAL rifle. All of them had the receiver bridges milled off to some extent.
the civilian version still retained the rear sight mounts, but everthing ahead of them was milled off.
Many civilian sporters also had the receiver bridges milled off.
The strength of the action isn't the receiver bridge per se'.
The rear locking lug fits into the side of the receiver, below the area that would be milled away. The other opposing lug fits against the opposite side, also below the milled off area.
The left side recess is hardened as is the rest of the receiver in that area. There is still a lot of strength where it's needed. Enough for the pressures and thrust developed by the 303 Brit cartridge.
If the receiver on the OPs rifle was milled below the rear sight base line, then there may be issues.
OP, IMHO, from your far to brief description of the metal removal, you don't have anything to worry about, other than you don't have a rear location for a scope base.
Does your rifle have a flip type tangent sight on the barrel, just in front of the knox?
What you're calling a "jungle carbine" may actually be an EAL rifle, which in VG condition, is quite collectible.