To add my $.02, I bought the 'EGR Blanking Plate Full Kit' from 'Phillipstuart33' on eBay. £9 inc P&P.
It's a plate, gasket and 2 (longer) bolts - with instructions. Delivery was next day.
The kit is actually designed to be inserted on the hose side of the EGR valve - leaving the valve in place.
I completely removed mine so used the new plate and gasket against the manifold (a la Difflock) but found even the existing bolts now slightly too long (or just not used to screwing in that bit further) so I used the metal gasket from the original to pack out a little.
I also bought a replacement top pipe from Allisport - again friendly, next day delivery but I was slightly taken back by the price - £50 for a hose. Bloody hell...
I soaked the bolts in WD40 the night before which was well worth it - by far the longest part was undoing them - grazed knuckles ahoy!
I left the valve's wiring and plug tucked in by the jack and sealed the now empty pipe hole on the nearby unit (?) with a bit of sealant.
Mine's a basic 97 manual 300tDi with about 128K. It wasn't blowing out smoke previously but did feel a little 'lumpy', particularly in the lower gears. When I removed the old top pipe there was an amount of thick black gloop, which took some cleaning - I advise gloves
I have noticed an immediate improvement in response - and not all that subtle like I thought it would be. Going through 1st and 2nd is definitely smoother and it pulls up hill much more evenly.
I've not had the Disco that long and have only ever measured the MPG over 50 miles, which returned about 23mpg. Not brilliant. I'll be interested to see what I get now - I'll do a more accurate reading over 200 miles next.
So, an easy job (I'm no mechanic) and an immediate benefit. Result
Now I want a new intercooler.........