From the FCO's website (www.fco.gov.uk). This is a summary, would suggest you read it all. I have quoted the info relevant to both St Petersburg along with the visa enquiry you asked about. None of this is meant to frighten you, but you need to be aware of the following:-
"There is a high threat from terrorism in Russia, including suicide bombings in public places. Attacks have occurred most frequently in Moscow and in the North Caucasus.
Around 215,000 British nationals visit Russia every year. Most visits are trouble-free. The main type of incidents for which British nationals require consular assistance in Russia is for registration problems or lost or stolen passports and migration cards. Be vigilant at all times and also watch out for pickpockets and street crime, especially in large cities and in busy areas, e.g. railway concourses.
We strongly recommend that you obtain comprehensive travel and medical insurance before travelling. You should check any exclusions, and that your policy covers you for the activities you want to undertake. Please see: Travel Insurance.
In St Petersburg there has been a sharp increase in street crime since April 2004, with tourists being targeted specifically. Since April 2005, the number of cases of tourists being held up at knifepoint on the metro and buses have increased. These crimes are carried out by well-organised gangs. You should be especially aware of pickpockets in the main tourist areas. Incidents of bogus police officers harassing and robbing tourists are also occurring. If you are stopped always insist on seeing ID. Avoid openly carrying expensive items, or anything that might easily identify you as a tourist.
There are a number of services offering addresses and contact information about Russian women who are looking to become romantically engaged with Western Europeans. A number of prospective suitors have entered into correspondence, only later to be defrauded. If this occurs, there is little that the British Government can do to assist in the recovery of any capital outlay. We advise that you enter into correspondence with the appropriate level of caution.
Political Situation
The next major elections scheduled are the Duma (parliamentary) elections in 2007, and the next Presidential elections are scheduled for 2008.
If travelling by taxi, use officially marked taxis and do not share them with strangers. We advise against flagging down unofficial taxis.
ENTRY REQUIREMENTS
All foreign nationals entering Russia must fill in a Migration card. These cards have recently changed from bilingual (Russian/English) to Russian only cards. Information in response to the questions on the cards can still be completed in English, however this is difficult for non-Russian speakers. A sample card plus translation can be found on the website of the British Embassy Moscow
The card is in two identical parts. One part will be retained by the Immigration Officer on arrival. You should keep the other part with your passport and show it, along with your passport, to the police if they stop you for an identity check during your stay. You should hand in the second part to the Immigration Officer on your departure from Russia. You must complete a new migration card each time you enter Russia, even if you have a multiple entry visa. If you lose the second part of the card you will be fined, and your departure from the country could be delayed.
Visas are required to enter Russia. During periods of high demand, for example during the summer holidays, you should apply for your visa well in advance. If you live in England, Wales or Northern Ireland you should apply to the Russian Embassy in London: www.great-britain.mid.ru. If you live in Scotland, you should apply to the Russian Consulate General in Edinburgh.
The Embassy in London can normally process visas in 15 working days, and you can submit an application by post or in person. If you want to get a visa more quickly it is possible to queue in person and pay an extra fee, though the numbers processed in this way per day are limited. You must have an exit visa to leave Russia. Most entry visas include an exit visa. However, some entry visas i.e. certain types of student visas, do not include an exit visa. If this is the case your sponsor, not the Embassy or Consulates, will need to obtain the exit visa for you before you can leave the country. Ensure that you are aware of the terms and conditions attached to your visa before travelling to Russia.
You must register your visa within three working days of arrival in Russia with the local branch of the Ministry of Internal Affairs. Most major hotels will do this automatically. If you are staying in private accommodation the owner of the property must do this for you. You need not register a visa if your visit is for under three days.
If your passport has less than six months to run, you may be refused entry to Russia. You are advised to get a replacement passport before travelling.
Single parents or other adults travelling alone with children should be aware that some countries require documentary evidence of parental responsibility before allowing lone parents to enter the country or, in some cases, before permitting the children to leave the country. For further information on exactly what will be required at immigration please contact the Russian Embassy in London www.great-britain.mid.ru.
If you intend to travel by train on popular routes such as Warsaw-Moscow or St Petersburg-Kiev you will need to obtain a transit visa for Belarus before travelling".