Williams is one of a record 13 Ospreys in the Wales team

The Ospreys beat Gloucester and the Blues overcame Bristol to make the European quarter-finals.

"The regions' success is a boost," said Williams, one of 13 Ospreys in the Wales team to face England on Saturday.

"We have beaten the top English sides so hopefully that will give us a psychological advantage for a change."

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Wales' Twickenham jinx extends back 20 years to when Adrian Hadley's try-double inspired the Welsh to their last victory at HQ.

But for the first time in Heineken Cup history two Welsh regions have qualified for the Heineken Cup quarter-finals.

"We've proven we're capable of big things," said 30-year-old wing Williams.

"The Ospreys beat Gloucester, the best team in England, and the Blues have thoroughly deserved their success.

"In the past we've struggled against the so-called bigger sides which may have affected Wales in the Six Nations."

Ospreys and Wales outside-half James Hook added: "Gloucester had a huge pack and the Ospreys took that away from them.

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"It was a wet day but their backs didn't function. We beat them in all aspects of the game and if Wales do that against England at Twickenham that would be half of the battle."

New coach Warren Gatland named a record 13 players from one region, the Ospreys, in his first Wales team that will open their Six Nations at the home of the World Cup finalists.

"It shows the faith Warren has in the Ospreys boys," said Williams, who will be the most experienced Welsh back on Saturday as he will win his 52nd cap.

"The Ospreys lads certainly deserve their place because we have been playing some fantastic rugby, but this is a Welsh team and not an Ospreys side."

The Welsh defence was criticised when they crashed out of the World Cup last autumn in the pool stages following humiliation against Fiji.

Coach Gareth Jenkins was sacked in the wake of their World Cup nightmare when pundits accused Wales of being a soft touch and making basic errors.

But Williams insists that Gatland's team will be hard-nosed as the New Zealander and his assistant Shaun Edwards have given Wales a much-needed "kick up the backside".

"It has probably been the toughest week I've had since I became a Wales player," admitted Williams, who has played for seven other coaches in his seven-year international career.

"It has been physical and we've had tough training but that was what we needed, we needed a kick up the backside as there is no more physical team than the English.

"I had to run straight into two big forwards and try to keep hold of the ball.