Can we select candidates for redundancy from amongst the part-timers, most of whom work for pin money?
Not if you select those candidates because they are part-time workers. Part-timers are now entitled to the same employment rights as full-timers and that includes the right not to be singled out for redundancy. It is unlawful to treat part-timers less favourably than full-timers, unless you can justify the different treatment on objective grounds. Moreover, if most of your part-timers are women, you risk being accused of indirect sex discrimination (see Discrimination).