I think the eTool default LCI database is a better choice than the BRE IMPACT database for an LCA in the UK if you are not trying to complete the LCA for BREEAM. The two main reasons I see for this are that the eTool default is more comprehensive in terms of the LCA modules included and also because the BRE IMPACT set is very limited in the service available (I believe it only includes solar panels, whereas the eTool database includes light bulbs, electricals and electronics, motors and so on).
It is true that there aren’t many UK specific templates in this database (at this stage), however in many cases it shouldn’t matter if the template was created in the Australian set as the materials data will update from the UK database (in terms of manufacturing intensities and transport impacts), so these will still provide an accurate representation of the material in the model. Having said that, there are some cases where this won’t be true, for example an Australian timber stud wall wouldn’t be code compliant in the UK because it isn’t thick enough for the level of insulation required. In this case (and others like it) the template would need to be modified for the UK.
Unfortunately there aren’t any templates in this database for UK energy and water use just yet, so I think the best approach would be to transcribe the information from the relevant templates in the BRE IMPACT data set into templates in the eTool LCI data set (UK). Those templates are fully referenced, so the information should be good quality.
There are some Air-to-Water heat pumps in the eTool default database. They are classified as hot water services. Look for “HWS – Heat Pump”; there is a large distributed system and a smaller domestic system available. If they are not appropriate for your needs let us know and we can see what else might be appropriate.