Why yes there is.
This UK government site will tell you if you need a visa to transit through the UK. You enter your nationality, desination, and any visas you already hold, and it will tell you if you need a transit visa or not. It also includes instructions for applying for one.
HOWEVER: There have been changes taking effect Dec 1 2014 to which countries' nationals require transit visas. Regardless of the link above, check this page for a revised list of which nationals need transit visas if they are passing through immigration (VIT - section 2) and which require visas if they pass through immigration or remain airside (DATV - section 1). Procedures remain the same.
Beware that the exemption conditions for visa-less landside transit are slightly different from the exceptions for Direct Airside Transit. As of this writing, the page linked above erroneously refers to a document describing the landside exemptions even from its section about DATV; refer to the The Immigration (Passenger Transit Visa) Order 2014 for the actual DATV exemptions.
As a summary (but check for exceptions):
- You must arrive and depart by air, and your outbound flight must be booked and confirmed.
- You don't need a transit visa if you would not need a visa for a tourist visit to the UK.
- A transit visa comes in two forms: Direct Airside Transit Visa (DATV) which is limited to 24 hours and you must remain 'airside' (i.e. cannot pass through immigration) and a Visitor in Transit Visa, which is valid for 48 hours and allows you to change terminals or airports.
- You must have all the necessary documentation for your final destination, including any visas.
- You are exempt from needing a transit visa under certain conditions. These can be found at https://www.gov.uk/check-uk-visa. As of 25 June 2015, the conditions are:
You might be eligible for ‘transit without visa’ if:
- you arrive and depart by air
- [you] have a confirmed onward flight that leaves on the day you arrive or before midnight on the day after you arrive
- [you] have the right documents for your destination (eg a visa for that country)
One of the following must also apply:
- you’re travelling to (or on part of a reasonable journey to) Australia, Canada, New Zealand or the USA and have a valid visa for that country
- you’re travelling from (or on part of a reasonable journey from) Australia, Canada, New Zealand or the USA and have a valid visa for that country
- you’re travelling from (or on part of a reasonable journey from) Australia, Canada, New Zealand or the USA and it’s less than 6 months since you last entered that country with a valid entry visa
- you have a residence permit issued by Australia or New Zealand
- you have a common format residence permit issued by an European Economic Area (EEA) country or Switzerland
- you have a residence permit issued by Canada issued after 28 June 2002
- you have a uniform format category D visa for entry to a country in the EEA or Switzerland
- you have an Irish biometric visa and an onward flight ticket to the Republic of Ireland
- you’re travelling from the Republic of Ireland and it’s less than 3 months since you were last given permission, on the basis of holding a valid Irish biometric visa, to land or be in Ireland
- you have a valid USA permanent residence card issued by the USA on or after 21 April 1998
- you have a valid USA I-551 Temporary Immigrant visa issued by the USA (a wet-ink stamp version will not be accepted)
- you have an expired USA I-551 Permanent Residence card issued by the USA on or after 21 April 1998, with a valid I-797 letter authorising extension
- you have a valid standalone US Immigration Form 155A/155B issued by the USA (attached to a sealed brown envelope)
You won’t be able to transit without a visa if a Border Force officer decides you don’t qualify under the immigration rules. You can apply for a transit visa before you travel if you’re unsure whether you qualify for transiting without a visa.
If you need more information than is provided by this website you will need to check with your airline or contact the UKVI. The Home Office's Charging Procedures - A Guide for Carriers also provides some guidance on the subtler points of the rules (it's intended for professionals, not passengers, but does explain in great details when a visa is or is not required).
Changes to the rules activating on 1 December 2014
A Statutory Instrument entitled "The Immigration (Passenger Transit Visa) Order 2014" will make large portions of the above text obsolete. Please refer to the instrument itself at http://www.legislation.gov.uk/uksi/2014/2702/made until further guidance becomes available. The government's interactive page, which leads the user through a series of questions will take some time to sync up with the legislation (if ever) and should NOT be relied upon after the 2014 order takes effect.
Note on UK Border Control
In London Heathrow, if you fly from outside the UK or Ireland and leave to another country (neither UK nor Ireland), it is possible to transit without entering the UK and going through UK Border Control, you can stay airside. There is no hotel airside, so if you want to stay in a hotel for an overnight stopover, you have to go through UK Border Control. There is a detailed guide available on Heathrow airport website.