Are these containers in the house, or outside? Most likely to be fungus gnats, although fruit flies can sometimes be an issue. Fungus gnats are more common in houseplant compost - the RHS has a page on fungus gnats, that's worth a read, but also, don't keep your plants too wet, let the compost dry out a bit between waterings.

Sorry Bamboo, for taking so long to get back to you. The plants are in the glasshouse for the winter, will be moved outside as soon as the frost passes. If it is fruit fly what is the best way to get rid of them. Bamboo sorry for being such a nuisance, I am grateful for your time, Thanks.

If its fruit flies being outside will get rid of them, but its much more likely to be fungus gnats. These are more prevalent because of newer potting compost mixes containing composted materials rather than peat - fungus gnat larvae like partially decomposed material.

Thank you Bamboo,