The 47-year-old from Leeds beat the likes of seven-times Crucible winner Stephen Hendry and former world champion John Parrott in Scunthorpe last season to lift the Seniors trophy.
Lines – in action today on the first day of the Dafabet English Open in Barnsley – was eligible to enter last season because he was not playing on the full-time tour.
But after a successful 2016-17 – which included a UK Championship win over Neil Robertson in York – Lines regained his tour card via the EBSA play-offs.
Rules prevent tour professionals from entering the Seniors, meaning Lines will miss the chance to retain the only major title he has won in over 20 years as a professional snooker player.
“I am not allowed to defend the title, because I am back on the tour,” said Lines. “I was hoping they were going to let me, as defending champion, but it’s only for players not on the tour.
“I am disappointed not to be defending the title. I absolutely loved it.
“I have been a pro for 20-odd years, but it’s the first sort of proper competition I have won. I am gutted not to be able to defend it.
“I spoke to (organiser) Jason Francis a few times, but he was adamant he couldn’t let any pro’s in it.
“That’s fair because there are a lot of pro’s who would have wanted to enter.”
A rejuvenated Lines is embracing life back on the circuit, combining his own career with helping out behind-the-scenes with son Oliver, the up-and-coming 22-year-old who looks set for a bright future.
Without the constant battle to stay in the world’s top 64, Lines has adopted a more relaxed approach. That’s certainly paying dividends, reaching the last 16 in both August’s Paul Hunter Classic in Germany, and then this month’s European Masters in Belgium.
“I got to the last 16 in Germany, last 16 in Belgium, and have been playing some pretty good stuff,” said Lines, who works part-time at the Northern Snooker Club in Leeds.
“I think it’s just I am more relaxed, enjoying it, just going to the competitions with Oliver.
“I have been working a lot with Oliver, a lot of my time gets taken up with that.
“I spent the last five or six years on the tour, looking at rankings, and in the end it drives you mad.
“Now I just go out and play. If I win I win, if I lose I come back to the club, do some coaching and get to work.
“I am still a world champion, there’s not many of them about.”
Lines heads to the Barnsley Metrodome this morning for a televised showdown with world No 7 Barry Hawkins in the first round of the English Open.
“We have played at the Metrodome a few times in qualifiers, but never in a full ranking event,” he said.
“I hope the fans come out to support us, the fans turn up and create a good atmosphere.
“Sport is popular in Yorkshire. Hopefully, Barnsley will be the same – events in Leeds, the UK finals in York and obviously Sheffield get crowds – and people will come to support the snooker,” he said.
Oliver, currently ranking No 62 in the world, like his father faces a tough opening round in Barnsley tonight, playing world No 13 Ali Carter.
The tournament – which has switched to South Yorkshire after being held in Manchester last season – starts today and concludes on Sunday, with a £70,000 top prize and the chance to win a £1m bonus if one player can complete a clean sweep of the four Home Nations events.
Other Yorkshire interest today sees Sanderson Lam – like the Lines duo, a member of Northern Snooker Centre – face China’s Chen Zifan, while Sheffield’s Adam Duffy, 28, plays Jimmy Robertson.
York’s rookie Ashley Hugill, 23, faces veteran Nigel Bond this evening.
Tomorrow, it’s the turn of Doncaster rookie Chris Keogan, 25, who tackles world No 2 Ding Junhui, while Pickering’s Paul Davison, 46, meets John Astley.
Leeds’s David Grace, 32, tackles former world champion Mark Williams.