I wish Plasplugs still made those chipboard plugs that glue in the ends of boards.
They made a much better fixing for screws and might be ideal for MDF.
They stopped making them about 1990 and when I found out I went round every local DIY shed and hardware shop buying up all they had in stock.
I got a bargain at B&Q as they sold me the last 12 strips for the price of 1 -40 plug strip.

Don't bother with them, split before I had tapped it all the way in!

JB.

thanks again for all your help people i have come to the conclusion as mdf is close pressed fibbers the only fixing that will work is one that doesnt displace more than 10% of the screw area and certainly wont work without a pilot hole as any screw will have to deflect the layers of the mdf because they cant deflect or compress the material
so unless there is a screw that can remove the material quicker than the screw goes in [imposible i think ]i will have to keep drilling and countersinking

funny enough keith thats one of the solutions i worked on too if the mdf delaminates when screwing take the screw out fill with glue put the screw in a few tuns[to stop the glue comming out]clamp tightly then screw home firmly

another point i alway slightly undertighten with the drill and finnish by hand because over tightening will again delaminate the mdf

I don't know if it would be applicable here, but some joints, such as shelves to uprights, can be made quite well with pocket screws, this way the screw is going into the side of the upright, rather than into the edge of the shelf. Much less troublesome.
John

heeelllooo seaco and welome thank you for your comments  

in general i was looking for minimum operations [movements]with maximum results will try plugs and fingers crossed may help but suspect the plugs may still delaminate the layers  
but thanks for the suggestion i will try it

Okay guys (and girls-well someone mentioned them!)
MDF screws, if you must use that dreaded material(me included lately) then why not try MDF screws, and here is the link!!!!http://www.quickscrew.com/screwmdfcskphillps.html  .. and yes i have used these, pilot holes a must .. read later in this posting

now then HM, the cam and dowel fixing is designed specifically for use in chip board type substrates due to the deep thread upon the dowel section, and would delaminate the mdf very rapidly,    

as for mdf fixings anyways, i once was given a fact sheet from one of my suppliers, which stated that any screw fixing must be countersunk, using pre drilled and piloted holes, due to the complete lack of compression available from the material...
hopefully this will help you guys(and girlies)
best regards 8) 8) 8)

i stand corrected upon the dowel /cam, i have always been advised by my suppliers NOT to use in end of mdf panels, as for the screws, they work for me, if you have any doubts why not give quickscrew a ring, and speak to them!!!