how can i fit a new stopcock?

I assume the one on the lead doesn't work.

MOST IMPORTANT IS DON'T PULL THE LEAD AROUND AS OLD LEAD / LEAD JOINTS CAN FRACTURE.
I assume the copper is 15mm. The 'push up/down directions are if the pipe is vertical like mine. Obviously changes to 'sideways' if horizontal.

FIRST CUT A V SHAPE IN A PIECE OF WOOD TO ACT AS A TURN OF KEY [MEASURE AGAINST THE HOUSE SC FOR SIZE OF V ] ON YOU GARDEN STOPCOCK IF ITS THE STANDART CAPSTAN HEAD AND NOT SQUARE HEAD TYPE.
SAVE PUTTING HANDS DOWN A NARROW PIPE FULL OF MUCK
Have a chat with your local plumbers merchants and tell them what the problem is and can you use the new braded flexible joiner of the push fit type. So what you need is
1, Stopcock, 1, Tube Fernox 3 sealing compound, 1 silver braded flexi fit pipe with releasable push fitting both ends, or if you can only get one with a releasable push fit one end and tap fitting the other ask the plumb shop for a connector that fits the nut with a compression joint the other end to fit the feed pipe [usually 15mm]. Now assembly. find the outside stopcock turn the water off. If you can't find it then in the street on the pavement will be another one. You must contact the water supplier as officially you can't touch them and they charge a turn off/on fee.
If you do a break it it will cost you hundreds. If they say you can turn it off then get the right tool for it[ some a standard head like the house one, others a square end] and get in writing from them a disclaimer of liability freeing you from any costs involved in replacing the street stopcock if you break it.
Proceed as follows once water is off.
Look at the side of the new Stopcock [SC for short] if their is a flow direction arrow on it the arrow points away from the IN flow ie: in the direction of feed. Place the SC on the pipe at this point the arrow doesn't matter. mark off on the pipe approx 75-100mm from the existing SC still holding the new SC on the or side of the pipe mark the other end. When you are sure the water is off get some rags and a bowl and make the first cut on the first mark made. once the surplus water has drained off make the second cut but make it about 25mm above the top mark. This should give you an off cut of pipe about 100-125mm long. If there is a flow direction arrow on the new SC the tail of the arrow faces the old SC. so take off the nut slide the nut followed by the olive over the pipe. Smear a little of the Furnox sealing compound around the first 10mm of the pipe, slide the SC onto the pipe ensure the pipe is up against the stop then draw up the olive followed by the nut and tighten the nut. Now you probably wont be able to put the offcut peice of pipe into the SC so pick up the braded flexi pipe and push the pushfit end onto the off cut of copper pipe up to its shoulder. no sealant required. Remove the nut and olive from the SC and slide the copper pipe on the flexi pipe into the SC up to its should/stop then attach the fitting supplied to the top [nut on the flexi pipe] Hold it in place and mark on the pipe just below the stop shoulder of the fitting you just put on the mark is where the next cut comes in. Remove the flexi pipe from the SC and cut the pipe [not the one on the flex pipe but the top half of the flow pipe].
now for a dry run fit the compression fitting on the upper section of the pipe ready for the flexi pipe. Slide the flexi pipe back into the SC and secure the top nut on the flexi pipe to the compression fitting make sure there is no strain on the flexi pipe, ie you don't have to pull it up to get it to fit. You should have a slight bend in the flexi pipe which is better than the pipe/s being to short. However if it turns out you HAVE cut to much off the top pipe then release the flexi push fit joint and if the second off cut is longer than the first use that on it and remeasure correctly this time. Assuming all is right remove the flexi pipe from the SC and slide the nut on the copper end followed by the olive and smear sealant around the end of the copper pipe and push it back into the SC slide the nut and olive down on to the SC and tighten. Then remove the upper pipe compression fittting leaving the nut an olive on the pipe. smear sealant around the end of the pipe and push the compression end of the fitting onto the pipe then slide the nut and olive down on to the fitting pushing the fitting up until it stops at the shoulder then tighten the compresion nut [Use two spanners/wrenches to stop the fitting turning whilst tighening it. You now have the flexi pipe dangling smear a small amount of sealant around the thread of the fitting and screw the flexi nut onto the fitting. Hey presto a new stopcock. And that's how I did mine.

Roy If you are unsure of the instructions e-mail me with your problem to remind me who it is and I will e-mail a drawing of what you need to do. let me know if the feed pipe is vertical or horizontal and facing it which side the lead is on. I will do the drawing according.
ALL SIZES OF PIPE ARE ASSUMING EXISTING IS 15MM.
robertwhiting76@hotmail.com I will check Sunday -Tues and if I don't get one I will assume you have done the job.
Sorry it's so long but you did ask for 'in detail'

Bob
October 2005