Both countries enter the home straight in terms of their preparation for next month's tournament with a double-header at Twickenham this weekend, then the Millennium Stadium on Saturday week.
Wales boss Warren Gatland and his England counterpart Martin Johnson intend naming their final 30-man squads for New Zealand on August 22.
And Cardiff Blues centre Roberts has backed Gatland's view that neither team will hold back in front of a capacity 82,000 crowd.
"There will certainly be no love lost," said Roberts. "There is no such thing as a trial England versus Wales game.
"Twickenham is sold out and boys are playing for World Cup places with the chance to realise dreams. It's also a capped international, and no player will disrespect that at all.
"We couldn't have asked for tougher opposition than England to help prepare for a World Cup."
Gatland will parade 11 of the team that started last season's RBS 6 Nations opener against eventual champions England in Cardiff, the exceptions being full-back Rhys Priestland, wing George North, hooker Huw Bennett and number eight Toby Faletau.
Fly-half Stpehen Jones wins his 101st cap, making him the most decorated Test player in Welsh rugby history, while flanker Sam Warburton is captain instead of an injured Matthew Rees.
Gavin Henson, though, has to wait for his pre-World Cup chance, which in terms of potential competitive action now boils down to just two games - England at home next week, followed by Argentina seven days later.
Wales' two previous World Cup warm-ups against England proved to be horible mis-matches, beaten 43-9 on home soil in 2003 and then thumped 62-5 at Twickenham four years ago.
Although Gatland was not at the coaching helm for either of those matches, memories still linger.
He added: "We know what happened in 2007, but also that Wales took a hammering at home in 2003, being absolutely mauled to bits by England up-front, so let's not forget that."
Wales will arrive in south-west London on the back of two punishing training camps in Poland, which has helped them prepare for a tough World Cup pool that also includes South Africa and Samoa.
"The boys have worked extremely hard but there is only so much you can do on the training ground," said Wales assistant coach Neil Jenkins.
"There is nothing like playing in matches, and we've got to hit the ground running.
"It's England against Wales on Saturday, and it will be massive. It is the ultimate game for any Welsh player to play in, and it's important that we are ready to go."
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