'Ashwin is the best off-spinner in the world' – Graeme Swann

"Ashwin is easily the best off-spinner in the world. His record in subcontinent is phenomenal and I loved the way he bowled at Edgbaston," Swann told the Times of India.

"Australia's Nathan Lyon has come up brilliantly and I am impressed by the fact that he has been successful back home. He hasn't been as effective in England and I would keep Ashwin just ahead of him because of the variations he has, in addition to being brilliantly consistent."

The 31-year-old India off-spinner, who has 324 Test wickets to his name, is currently playing in the five-Test series against England. He has picked up eight wickets from three Tests so far even as his side lost the first two games at Edgbaston and Lord's but won the third at Trent Bridge to trail England 2-1 with two games to go.

Swann, who played 60 Tests and picked up 255 wickets with his off-spin, spoke highly of the young Afghanistan leg-spinner too. "Yes, [Ashwin] is the best in Test cricket, but in T20s you can't look beyond Rashid Khan. He has a fast arm, a great googly and a brilliant story as well," Swann said.

"Rashid is just a very exciting cricketer and I would love to see him be successful in Tests as well, as and when he gets to play regularly."

The 19-year-old Khan has taken giant strides since his international debut in 2015 and is currently the No.1-ranked bowler on the MRF Tyres ICC T20I Rankings. He has 64 wickets from 35 T20Is and picked up seven wickets from two matches in the recent T20I series against Ireland, which Afghanistan won 2-0.

While the subcontinent nations have had spin has their strength over the years, for England it has been a bumpy ride ever since Swann retired in 2014, as they have not been able to find an all-conditions spin bowler in Test cricket. Moeen Ali, during his breakthrough season in 2014 where he was successful against the visiting Indians, was seen as a long-term option, but his form overseas hasn't been the best and he recently lost his place in the England side after the first Test against New Zealand earlier this year.

"Yes, we have struggled, but Moeen is a good spinner, but I think he doesn't believe he is a good spinner," Swann said of Ali. "Unless he gets the belief back with the red ball, he will never be able to do the job in Tests. He needs to have more revs on the ball to get the batsmen out."

Ali is in the squad for the fourth England-India Test, which will commence on 30 August in Southampton.