Clare, I really don't see how a WiFi repeater will get the signal through your thick stone walls.

Nontek's suggestion is probably the best one as it'll use your mains wiring to get the Internet into your shop. However, because you've got a laptop, you may want to use it wirelessly so a pair of these may be more suitable. You simply plug one into the mains socket near your router then attach the router to it with the supplied network cable. In the shop you plug in the wireless unit into any available mains socket and a new wireless network will be available for your laptop with no unsightly cables to be seen anywhere.

One word of warning caution though - powerline adapters don't always work reliably when they're plugged into those electrical power-strips with multiple sockets. It's always best to plug each unit into its own socket on the wall.

Will a home-plug in the house and the shop do the trick? ..... Yes!

Also very easy to set-up, just Plug and Play. One plug goes into a mains socket near the Router and is connected to Router via ethernet cable (which is provided, for each plug bought), and then another plug can be inserted in any Mains socket anywhere on the same ring-main, which in turn is connected to laptop via supplied ethernet cable.

'BT telephone line is split by the engineer who installed it into a telephone line and a broadband line at its entry point to the house'

Not strictly true. Normally the phone line terminates in a master socket into which a filter is plugged. It is this filter that splits the broadband (ADSL) and voice. Some master socket faceplates have a built-in filter and a twin socket faceplate - one for phone and one for broadband. You cannot plug a second router into a phone extension - only one router per phone line.

So, Homeplugs are the best way to go.

'However you can EXTEND the ADSL socket using proper cabling'

I understand what you mean, now. It is also possible, of course, to run an ethernet cable from a spare port on the router to elsewhere. However, as she wants to avoid cabling, the Homeplugs are probably the simplest option.