HI
If you are a member of the ISCP and your residence is in Ireland then under the terms of your insurance policy which is separate from your membership fees then you may practice in the private system in the UK for a period of up to 6 months. However if you wish to work in the public sytem you must be registered with the HPC and to use to the UK suffix MCSP you must be recognised by the CSP.
However, the point I really want to highlight with you is that please stop seeking ways to screw the system and to avoid having your qualifications recognised. These systems are in place to ensure that standards are met and that does who are not suitably qualified to practice do not.
If your qualifications are not good enough, then you cannot practice as a physiotherapist.