It was a big shock last December when Clash founder Joe Strummer died unexpectedly of a heart attack at age 50.

Thankfully, he left behind some new music.

Fans of his politically charged rock can hear the final tunes he recorded with his post-Clash band, The Mescaleros, on the group's third and final album, Streetcore, which hit stores this week.

"He sounds youthful, he sounds energetic, and he was," said Scott Shields, The Mescaleros guitarist and Streetcore's co-producer, down the line from London this week.

"(The new song) Coma Girl, for example, was cut live in the studio and that was a one take and that sort of epitomizes what he was doing. He was performing that song. He was stamping his feet. He was playing his guitar. It was like a performance in the studio. It was like watching a gig."

But while it may be reassuring for some to hear Strummer at the top of his musical game again, it was difficult for Shields, who took it upon himself to help finish Streetcore, which was only about six songs done at the time of Joe's passing.

"It was not therapeutic, that's for sure," the Glasgow-born musician said. "It was really hard because literally we went in two weeks after Joe died and assessed the situation. I think it was like a knee-jerk reaction for us, like, 'What are we going to do? Well, we better get in the studio and finish this off because that's what Joe would have wanted.' Basically, it was difficult because we had to keep the integrity of what we were trying to do in the first place. I didn't want anybody to have the option of being able to say, 'Oh, it just sounds like they've done that after he died.' "

And, no, once Strummer was gone, there was no spiritual guidance from the great beyond.

"No," said Shields with a chuckle. "I felt like if I ever saw him again, I'd give him a smack for leaving us. We had the choice to make it or not and the right thing was to make the record, but it was a difficult job, emotionally as well as physically. I'm a lot better about it now. There was a period, a couple of months after we'd finished the record, and we had some interviews to do, and I couldn't do them, to be honest. I'd get halfway through and I'd get all tongue-tied and flustered and anxious."

The biggest surprise was the discovery of some songs that Strummer had been recording with American producers Rick Rubin and Danny Saber.

Thus, a cover of Bob Marley's Redemption Song ended up on Streetcore from the Rubin sessions. The Strummer-Saber track All In A Day was also included. So was Strummer's own Long Road, which he had unsuccessfully pitched to Johnny Cash.

"It all sounded very in keeping with what we were doing on the record," said Shields, 33.

"I don't think Johnny Cash understood (Long Road). Joe told us (Cash) said something like, 'I don't understand this boy.' "

STRUM ALONG: The Crooked Beat Revue, a tribute to Joe Strummer featuring 17 different bands, takes place Dec. 6 at the Horseshoe with tickets available at the door only.