I am an Indian citizen and I do not qualify for DATV concession. Going for a trip to UK and Europe, I am having Multiple entry valid Visitor visa for UK. While on my way back from Paris I will be transiting in Heathrow airport. Do I need to take a airside transit visa even though I have a multiple entry valid UK visitor visa?
No, you don't need additional visa. From UK Border Agency:
Visas are valid for an unlimited number of journeys within the validity period of the visa.
People holding visit visas can only remain in the UK for a maximum of six months on any one visit, or until the visa expires if less than six months. This restriction is indicated on the visa by the entry ‘180’ days after the ‘Duration of stay’ section.
Holders of long term visit visas must still meet the requirements of the Immigration Rules each time they enter the UK. They must not be using the route to live in the UK for extended periods. If it is apparent this is the case Border Force officers must refuse entry to the UK.
So you can see there is no restriction for minimum period of stay and you can use your visa for a transit.
In addition to @Dirty-flow's answer, The general visitor visa is mandated for a land side transit which is greater than 48 hours and can be used for lesser than 48 hours landside or airside transits as well.
Additionally for reference the don'ts on the UK Gov website do not prohibit the use of the visa for such purpose either.