Parmaji
Speaking from personal experience, there are a few factors to consider here.
Firstly, I think there is a massive difference between a Sikh prisoner in a repressive country being held for his beliefs, or being held under false charges, yes these Sikhs need the utmost help and support from the community, there is no debate about that.
However if we are talking in the UK, then I think you will find most imprisoned Sikhs have been sent to prison after a reasonably fair trial, and more often than not, for a crime. I have spent time in a UK prison, 4 weeks, to be exact, the result of driving to Stansted airport the day after being banned from driving, and that at double the speed limit (so no miscarriage of justice here, I was young and stupid).
Of course prison is a massive shock to the system, but I think most Sikhs in UK prisons are probably there for short periods and for petty crimes. The authorities, and this is going back 20 odd years, were extremely fair, and in those days, we were all encouraged to go to the church on the Sunday, do not recall any other services for any other faiths.
A catholic priest did do the rounds of all the prisoners, regardless of faith, and came to see me eventually. An old irishman, he was a source of great comfort for me, in fact, the first time I met him, and having had time to reflect on the paths I was following, I was consumed with the desire to better myself, so I asked him if I could confess 'everything'. After 15 mins he started to look at his watch, after 30 mins, he started to look at the door, after an hour, he said he had to go, but, I replied, I am not even close to finishing, he took my hands firmly, looked me in the eye, and said 'son, you need to find your own God'. At the time I assumed he meant that I needed to pray to the Sikh God, but years later, I realised he meant I needed to find the God within, the Godhead if you will,
Amusingly, I noted I was watched constantly by a gang of skinheads, I walked around with my topknot in a hanky most of the time, so I was visual, but I was losing weight, so walked around with one hand on my jeans to keep them up, one day they surrounded me on the landing, and the leader came up to me, 'your jeans are loose', he said, I nodded, 'We've made you a belt from our laces, he said, and they proceeded to tie it round my jeans, and after admiring my new belt, melted away
I sympathise with anyone who is innocent and in prison, but if you are guilty and in prison, best just to get on with it, and pay the price for your crime