<whatsmyip will only report the public ip which is on the first routers wan port. It doesn't report what is on the 2nd routers wan port.>
With the first router set as a firewall (full security or selected ports open) it functions as a DHCP server and allocates an IP address in the range 192.168.1.X. This is shown in the first router's IP table. This is also reported as the IP address of the WAN port on the second router.
With the first router set with all ports open to the second router, it allocates its own public IP address to the second router (behaviour which has me baffled). This is reported in the first router's IP table and as the IP address or the WAN port on the second router.
I am not an IT professional but have spent the past 25 years configuring, integrating and supporting a wide variety of industrial control equipment. On a few occasions, I have wasted huge amounts of time trying to do something for the first time with equipment I have never used before which stubbornly refused to work, only to find out in the bitter end that the (brand new straight out of the box) equipment was faulty. My current VPN scenario definitely has that feel about it. I am certain all the advice I'm being given (your good self included) is correct.
Please would you recommend an ADSL modem and a VPN router (or an all-in-one unit) so that I can start again from scratch? Everywhere I look, I am getting the same advice on how to get our existing kit working - but it doesn't work. A new bit of kit is a tiny fraction of the cost of the hours already spent to no avail. I need to get something working and it doesn't have to be the stuff I already have on the shelf. Many thanks in advance for your advice.