I have just come back to Spiral Knights after about 6 months. Never have I had any problems in the past running the game. I entered the clockworks last night and had serious problems with either lag or fps drops. When I hit an enemy it would take a couple of seconds to register which obviously makes arena's etc a little tough.
Is there anything I can do to fix this?
You should firstly check your graphic settings, you are able to choose quality from low, medium and high, of course setting it to low will reduce lags. Also there is recently added option to incrase antialiasing. Setting it to lower value should reduce lags.
You should also look for your java software update.