The front of my bike feels a bit jittery, like something is loose (but it isn't) or there is a bit of play somewhere.

Wheel feels OK, and I'm sure the forks are ok as they are 2 months old Fox 36r's

Is it my headset bearings?

Put your front brake on and rock the bike back and forth. Test for any movement with your fingers (but be careful not to trap them anywhere) between the stanchions and the fork brace. At the lower and upper of the headset. Around the disc rotor, and caliper. Even the pads rocking within the caliper. Basically anywhere that bolts, slides, or rotates.

It could even be the bushings in your rear suspension?

have a play with your rebound settings on your forks, a couple of clicks out from the slowest to start with.

It could be that your forks need bleeding. Have a look at the TFT page about Fox forks. i think there's a "loose" bit at the top of the stroke with fox 36s.

Wheel bearings had it?

Quick release is done up tight, isn't it??

Could it be that you're just not used to the 36's yet? Bigger forks mean less weight on the front and potentially less grip on the corners.

With checking headset bearings, turn your forks 90 degrees to minimise fork movement.

Do the front brake on rocking thing as described.

Usual suspects:
Loose headset (probably that)
Loose QR
Loose brake caliper

Less likely:
Worn/broken headset
Cracked frame

Can also be something not on the front of the bike at all.

But its probably the headset.

Are they hope wheels ? With 36's, a few of us have found, that there can be a wobble when using hope pro2's on 36s. Does the wheel move latterally ? flip bike upside down and see if there is a wobble. Does on mine sometimes, have to kinda pre-load it tighten the axle up.

Top answers everyone but i think I have the answer thanks to TFT and Onzadog

My Forx clunks over small bumps which feels like a loose headset – what's up?
This is a common characteristic caused by a combination of the cartridge base valve hysteresis & bushing play. The bushing play is addressed by Fox as being down to the 'hydrodynamic lubrication' & the allowable clearance between the upper tubes & the bushings. We can often improve it considerably by bushing refitting/resizing to maximize the performance of the chassis. Add a little rework of the base valve & the jobs a good'n.

it is the front wheel bearings

Superstar 20mm hub… say no more.

its done OK though (for 20 quid) with probably 8 months riding in it plus 4 days downhilling in the Alps last month.

£5 gets you some new bearings. good as new