Rare indeed is the Welsh rugby autobiography that reveals how a corner of Adolf Hitler’s desk ended up in the family home in Newport or details how the author drove Lana Del Rey around Monte Carlo in a Rolls-Royce Wraith after she and Bono had watched him play paddle tennis with Prince Albert of Monaco. If Jamie Roberts achieved plenty on the pitch, few modern players have a wider-ranging story to tell off it.

We have not even mentioned playing guitar on stage with the Manic Street Preachers in Australia during the 2013 Lions tour. Nor Roberts’s impressive academic credentials as a qualified doctor and Cambridge University postgraduate student with four degrees. There are players with a hinterland and then, in a completely different league, there is the nearest thing professional rugby has to a renaissance man.

It is to the credit of the 35-year-old and his skilful “ghost” Ross Harries that Centre Stage: My Life in Rugby seamlessly weaves together all these contrasting threads. As a player, the former Lions centre always enjoyed a challenge – “I had a weird obsession with pressure, I only felt at my most complete if my life was full” – and found the book “a cleansing experience” in unexpected ways. “As rugby players you keep a lot in emotionally during your career. Rugby elicits every possible emotion … happiness, sadness, jealousy, resentment. You suppress the ones you don’t think are conducive to team sport.”

Now, though, Roberts has much to say on various subjects, not least the Welsh Rugby Union’s 60-cap rule designed to keep home-qualified players in Wales. Having plied his trade in both hemispheres, Roberts calls it “outrageous” and believes it crushes people’s sense of adventure. “It absolutely breaks me. Who are the WRU to deny players that opportunity and basically blackmail them for the Welsh jersey? I hate the thought of a young Welsh player having the chance to experience rugby in France or England and being afraid to do it because he’s not then allowed to play for his country. I think it’s absolutely berserk.”

Nor does he have much time, either, for the orthodox view – “It’s bullshit” – that training and thinking about rugby all day, every day is the only way to prepare effectively. In 2009 Roberts was part of a Barbarians side that, after several long days of drinking, beat the All Blacks at Twickenham and the moral of that story has always stayed with him. “I learned that if you flick the switch on a Saturday morning you can deliver, even against the All Blacks at a sold-out Twickenham after you’ve been desperately hungover. Rugby’s a monotonous job. You’re in the gym every day, doing the same weights. If you just do it relentlessly every day you get worn out and bored. For me it was about being busy in the week. The more I thought about rugby, the worse I played.”

Fascinating. He is similarly revealing on the subject of Warren Gatland. Roberts played under Gatland for Wales and the Lions for a decade but reckons he “could probably count on less than two hands the number of times I had an in-depth conversation with him”. More normal was a terse one-liner if their paths crossed in Wales’s hotel in the Vale of Glamorgan. “One day he was coming one way down the corridor and I was coming the other. He just looks at me and goes: ‘Jeez, Scott Williams trained well today.’ Before I‘d opened my mouth to reply he’d gone.” He later discovered the management were reluctant to praise him openly, believing he played better if he felt under pressure for his place. “Warren was very smart at pulling the strings. He understood how to get the best out of his players. It was all about winning, there was no room for sentiment. He’s far smarter than a lot of people gave him credit for.”

Rugby fans will also be interested in Roberts’s view that England could win the 2023 World Cup if they play Manu Tuilagi at 12 as a hard-nosed arrowhead. “I don’t think you play Marcus Smith, Owen Farrell and Henry Slade. You need a focal point.” If anyone should know it is the centre whose intuitive midfield partnership with Brian O’Driscoll on the 2009 Lions tour was not, he says, quite what it seemed. “He was a wonderful player, one of the best to have played the game. Skilful, quick brave … he had all the attributes. But what set him apart was his ability to communicate on the pitch, to see the picture, process the information and make the right call. I’ve not played with anyone else who’s had that ability.”

So, with the bizarre mystery of Hitler’s desk solved – Roberts’s paternal grandfather was in Berlin in 1945 and brought home a keepsake from the Führer’s abandoned office – what about rugby’s most pressing current debate? Given his medical training, few current players are better placed to discuss head knocks in rugby and, sooner rather than later, he predicts concussed players will have to wait longer than six days to return to play. “It doesn’t sit well with me. I think it has to be two weeks, I really do. I’ve been that player fighting all week to pass my protocols because you don’t want to let your teammates down. That decision should be taken out of players’ hands.”

But, then again, neither is he convinced that cases of early onset dementia affecting a number of players are yet definitive proof the whole of rugby is on a road to hell. “From an evidence-based medicine approach we’re in very dangerous territory if we’re saying: ‘It was definitely rugby that caused it.’ There are so many other possible factors: dietary factors, genetic factors, depression, lifestyle. On the one hand we have a group of rugby players who have these symptoms. On the other we have a huge cohort of rugby players who’ve had many head collisions who haven’t.

“Until the first cohort of professional players donate their brains, there is no way of drawing a direct link. There needs to be more research funding to allow us to better understand it. I am definitely not in denial but we need to work far harder to prove it is rugby that causes this.” At least one thing is already clear. If Roberts ever wants an influential role in rugby administration, it surely awaits him.

Centre Stage by Jamie Roberts is published by Hodder & Stoughton