Two small pensions what to do

Need some advice. I have got two small pensions and am due to start a new job with the local government. First one waswith the local government scheme about 3 yrs membership deferred pension. Left in 2003. Second one with nest about 6 yrs membership and still with them. There is a big gap with pensions contributions as have been doing agency works most of the time. Since I am a late contributor in my late thirties I am also thinking of AVC but am not sure how this works. Can this be done through my employer? Thanks