Osma do channel covers for their 450mm chambers, although the catalogue price is rather eye watering... (£145.50 each!) Osma also offer various 315mm dia chambers, including an option for 45 and 90deg connections on one side only, part numbers are 4D933 for L/H entry and 4D934 for R/H entry.
Building control may not have an issue, (they may not even see the issue on inspection), but a build up of crud is not desirable. A, it'll soon stink, and B will eventually dislodge and possibly then block the chamber....
I know of one contractor that has recently removed a few plastic chambers at a hospital and replaced with precast concrete, in order to give a smoother flow through the chamber and prevent any further issues of this type happening.
Building control may not have an issue, (they may not even see the issue on inspection), but a build up of crud is not desirable. A, it'll soon stink, and B will eventually dislodge and possibly then block the chamber....
I know of one contractor that has recently removed a few plastic chambers at a hospital and replaced with precast concrete, in order to give a smoother flow through the chamber and prevent any further issues of this type happening.