When does it become compulsory for breeders to microchip their litters please?

I'm going to view a litter in a couple of days but the advert doesn't say anything about the pups being microchipped before they leave,i know in the future it will become compulsory to have the breeders details on the microchip register as well as my own but just wondered when this would come into practice. For some unknown reason April 2016 comes to mind but I'm not sure.

Yes it is April 2016.

Many thanks Goldmali. I'm soo excited,its been a long time in the making (a year,which might not seem long to some though),ive been on a waiting list for nearly a year so I'm just getting a list together of all the appropriate questions to ask because knowing me I know as soon as I see them my mind will go all mushy and blank. Hopefully if all goes OK I'll be bringing home a new puppy to become a much loved member of our family in a couple of weeks. Fingers crossed.