Hello I am a solicitor with 20 years experience. I will try to help you with this question.
When a defendant is sentenced to a period of imprisonment then he will usually serve not more than half the sentence in prison and will serve the rest on licence under the supervision of the probation service. This is standard in all sentencing and Judges tend to state it in open court so that the Defendant knows precisely what he is being sentenced to.
He could be out a little before 3 years but it will not be much before. (unless there is a prison overcrowding crisis and the government decides to allow earlier release on tagged curfews).
It will be more comfortable and relaxed and mostly occupied by low risk offenders an those awaiting release. It will be a great improvement on the usual remand prisons like Pentonville or Wormwood Scrubs.
The phrase "straight sentence" has no legal meaning. Perhaps whoever said it was simply meaning not suspended.