litter training

My two have always been very well litter trained ever since we first adopted them, but just lately they seem to scatter poo everywhere (although i think its mostly Minstrel)! They always wee in their litter trays and mostly poo there too, but there is a high occurunce of just pooing where ever and it's really annoying, especially when I want to bring them inside for an evening :? especially when they never used to make such a mess!

What's the best way to deal with this????