As a rule of thumb we are told to never use restraints involving strangulation/choke techniques. The reasons are, I think, quite sound: potential for permanent serious injury/death and witness perception being foremost. Obviously if the situation is extremely serious then, to a certain extent, the ends justify the means; but there is no way the HO would shoulder any responsibility for a bobby strangling a DP.
Unfortunately the bottom line is that the point of teaching restraints etc. in the UK is to negate the need for the job to defend against litigation.