Hi Carylnz , Thank you for your response concerning my enquiry especially for providing the links which I found most helpful in reaching a conclusion. Though these pumps appear to be no longer being manufactured, there are a number of them still available either as old stock, or second hand but most are only suitable for running filtration in one or two aquariums and with the power consumption of each pump at around 30 to 40 Watts per hour, to use them to produce 40 to 60 lts of air per minute would render the running costs prohibited.
I have since discovered a range of pumps manufactured by a company named Techno Takatsuki Hiblow, usually referred to as Hiblow, which are readily available in the UK and Ireland. They are not a linear piston pump but a linear diaphragm pump which the manufacturer claims to be a perfect solution for applications such as domestic sewage treatment and fish-keeping where air flow is required 24/7, 365 days per year.
The Hiblow HP 60 XP series seems to be well rated as a reliable air pump and consumes only 39 Watts per hour which make it a very attractive choice against other competitors. I also not that it gets a mention in one of the web links you provided. So except someone can persuade me of something better this will most likely be the choice. Any further comments welcome.
Thanks again for you help.