www.climbout.co.uk
If the installer does not do this, then you will have to get the local building inspector around to check them & this will cost you a fee.
To find fully certified installers and free quotes for windows & doors you can visit this site: www.upvcwindowsfitted.co.uk/how-much-do-upvc-casement-windows-cost
you may find that double glazed windows prices in London are somewhat higher than those in areas with a lower cost of living. see more here: www.doubleglazingpriceguide.org.uk/how-much-do-front-and-back-doors-cost
Good question. The answer to “how can I get double glazing prices” is best found on a good quality price comparison website. like www.sashwindows-prices.co.uk/how-much-do-replacement-windows-cost