Simon Williams is Sir Humphrey in a new version of Yes, Prime Minister. Roz Laws reports.

As a young actor, Simon Williams was happy to show his public support for the Liberal Party.

He spoke on the hustings for his friend, broadcaster Clement Freud, who was an MP in the 1970s and 80s.

But times have clearly changed, because now Simon declares that politicians are “devious, wretched people”.

His low opinion is partly coloured by his current role – he’s playing scheming civil servant Sir Humphrey Appleby in the stage version of Yes, Prime Minister, which is on its way to the Birmingham Hippodrome.

The writers of the hugely successful BBC series have reunited to update the witty interaction between Sir Humphrey and Prime Minister Jim Hacker, played by Richard McCabe. They now exist in a world of spin and Blackberrys.

“It’s been brilliantly modernised,” says Simon, 64, best known for his TV appearances in Upstairs, Downstairs, Don’t Wait Up and Holby City.

“The audience is united in its distrust of politicians. We don’t quite know what party Jim Hacker belongs to, but the point is that all MPs are the same – they’re all devious and only interested in staying in power.”

Despite his cynicism, Simon urges everyone to vote in today’s local elections and especially in the referendum on the Alternative Vote.

“It’s vital to use your vote, whoever you vote for,” he says. “In the old days, people who hated politics would opt out by voting Lib Dem, but you can’t do that now. We don’t have any choice but to choose the lesser of all the evils.

“I have been very involved in the Liberal Party, but it’s a very different situation now.

“I’m not sure yet how I’ll go on the AV issue, as I’ve not been persuaded either way.”

Sir Humphrey is a master of manipulation, baffling his opponents with technical jargon and clever talk. Surely his long speeches must be hard to learn?

“Absolutely. And I can’t ad lib, because we depend on each other to deliver the right lines. Sir Humphrey is a terrible old windbag – he imagines that he will win the day by wearing Jim Hacker down with double-speak – but these convoluted speeches are so well-written that they are quite fun to learn.

“They are both such good parts. If I had a good enough memory, I’d love to swap roles and play Jim Hacker on alternate nights, like Benedict Cumberbatch and Jonny Lee Miller in Danny Boyle’s Frankenstein. But I simply don’t have the memory power.