Hi
Will a lot of unapplied modifiers maybe cause a scene to start to lag?
Regards
Shaun
Yes. A lot of anything will eventually cause the scene to lag. However on most newish hardware these days it is not uasually a problem. Why do you ask?
Hi MartinZ
Busy with a model that only has 290 000 verts at the moment, checked my machine before and only starts to lag at about 18 000 000 verts so I am sure this is not the problem. Maybe I did not explain properly in the OP, what seems to happen every now and again is that the scene hangs, circle turns for a couple of seconds before going back to normal. Does the same thing every now and again when using numpad to change ref pic views.
Modifiers was the only thing that I could think of?
Regards
Shaun
It can be a whole lot of things. It’s hard to tell without seeing the scene and knowing the hardware. It should not be modifiers unless you have really a lot of them or something obviously crazy like a few subsurf modifiers with 6 subdivisions. I noticed high resolution photographs sometimes have this effect. Do you have some reference photos loaded straight from a DSLR camera - 20 megapixels or more maybe? Maybe you are viewing a lot of textures in ‘Material’ viewport mode? You could also just gradually remove stuff from the scene to see when it stops lagging to find the cause.
Thanks MartinZ, thought it might be something simple 
Will have a go with the process of elimination. No subsurf, try not to model with it and also no textures at the moment.
Ref pics are some I bought online, I will see if they may be causing issues. Thanks for you time!
Regards
Shaun