as i understand the situation, if you take the organized ships tour then there is no reqiuirement for a visa, if youu want to do your to do your own thing you will need a visa a figure of one hundred pound seems to ring a bell

If you take the ships tours, or if you book tours through a recognised Russian tour agent like Alla, Red October, Den Rus or Anastasia, then no, you do not need a visa. You cannot step off the ship independently or outside their tour times. Doing your own sightseeing is not recommended unless you speak fluent Russian. There are no cabs allowed in the port area, and there is very little english spoken

I believe that if you wish to travel independently around the city then YES, but if you are happy just to join, and pay for, an organised ships tour then the answer is NO, as the ship will organise a group visa for the whole tour. Happy cruising