After a few more hours of tearing my hair out I've made a bit of progress.
The '400' error pop-up was because measurements are taken twice daily so on the source worksheet the date was merged over two rows for each day. The merging has been eliminated, the date now shows on every row and the '400' error pop-up no longer occurs.
As a result I can successfully now copy filtered data to the summary sheet using:
The area where I still require help is to amend that coding so that instead of being copied to a specific cell address it is copied to the first blank cell in col A below the existing data. I've been experimenting with End(xlUp) and End(xlDown) and Rows.Count and more but so far I've not been able to make it work.
Assistance with this will be much appreciated.