Erm! how about seam welding it ie place it over mine and weld it with lead,not the way its done know ie he's created a folded over lap joint.
I've found the ost sensible post so far...not in here mind.
Hi. There are a few issues shown on the images. This type of gutter has little or no fall. When lining this gutter with lead sheet, an allowance must be made for the expansion of the lead, if this is not done you will find it will fail in a few years time owing to metal fatigue. (creases turning to cracks). If using code 5 sheet lead the max length of any one piece should not exceed 2 m. I.5m if code 4 is used. It look as if the sheet lead has been rolled out its full length with out any thought about expansion?I also note the lack of lead clips, used to hold the front edge in position, to prevent wind lift. To over come the expansion problem and the jointing to the property next door a product is readily available (T Pren) which is neoprene bonded to two pieces of lead sheet. These are cut to the width of the gutter and welded into position, starting at the adjoining property and every 2 m thereafter. Good Luck