VARIETY is supposed to be the spice of life, but that particular commodity is sadly lacking in the ingredients of the star-studded bill at the London Palladium. Not until Peter Noone and Herman's Hermits get well into their act at the tail end of the show does any real spark of life become apparent.     Pop fans are well catered for with Noone. Roger Whittaker and, to a lesser extend, Russ Conway, comedians Dick Emery and Larry Grayson provide plenty of laughs. The evergreen Clark Brothers and the Doriss Girls leap about all over the place, while Susan Lane proves a huge success with her "quality" singing. But there is still an overall feeling that someone has assembled a safe bill and not taken any chances.     Peter and the Hermits work particularly well, fitting eighteen songs into a forty-minute act. They work very hard and a lot of the group's former amateurishness has given way to a good degree of professionalism.     Peter throws off the disadvantage of a weak, show-bizzy number at the opening of his act with solos on "Everybody's Talkin'" and "Little Green Apples," before the Hermits join him for a medley of hits including "I'm Into Something Good," "Years May Come" and "Sentimental Friend." In a smart black velvet suit, Peter sang very well and showed his flair for comedy when he dedicated a long routine to London, which he now regards as his home.     "Lambeth Walk" is turned into a splended production number - the Hermits dressed as pearly kings dancing with four girls - Noel Coward's "Pride of London" getting a good reaction and "Fish and Chips" providing plenty of laughs and even audience participation.     Peter sang part of "What Now My Love" in

French (thanks to Mireille's coaching?) and played flute during "Love Is Blue." The Hermits tempered their sound so as not to appear obtrusive while at the same time providing a good backing.     Roger Whittaker is in the Val Doonican-Andy Williams class when it comes to taking things nice and easy. Even on up-tempo numbers like "Michael" he appears very relaxed, but his audience's attention isn't allowed to wander.     Predictably, he sang "Durham Town," "New World In The Morning" and "I Don't Believe In If Anymore," each number receiving a very good applause at the beginning and end. He tried to teach the audience how to whistle in an East African manner by pouting their lips and sucking in their breath, and when they failed he showed how with a humorous native-type piece, "Mexican Whistler."     Returning to the Palladium after four years, Russ Conway proved that he has lost none of his style. "Lara's Theme" (marred by an insensitive brass section) and an instrumental version of "Love Is All" were performed beautifully, the audience appreciating every note.     A new Norman Percival arrangement of "Fool On The Hill" was both attractive and swingy and "The Christmas Song" proved apt for the time of the year.     Russ told a few gags, seemed understandably to be slightly nervous, but got through it all with honours. It's good to see him back.     Cries of "more" came at the end of Susan Lane's polished act during which she sang "Tonight," "the Impossible Dream," "I Could Have Danced All Night" and "And This Is My Beloved." She has a fine semi-operatic voice and seems destined for a big future.     On the comedy side of things, Dick Emery shone as usual and got a few belly laughs with a number of risque jokes, and Larry Grayson made the most of high campery to a good effect.     Finally, Pete Murray. It is kindest to say that his compering skills matched his "Golden Shot" debut last week.