I see that MyMemory (UK) is now stocking Anker products at good prices (free delivery too). They currently have the Anker 3A PowerCore 10400mAh Portable Power Bank with PowerIQ for £11-39p (or 2 for £22) with discount code VC5:
Other Anker products from MyMemory listed below, the Eufy Genie is also a good price at £24-99p
https://www.mymemory.co.uk/brands/anker.html
Note: I suspect the guarantee may be 12 months instead of 18 months (as shown in item descriptions).