Do Electrochains have a physical shop? I can only see a mailing address on their website, not an address where you could take your bike for service. If they are as they claim authorised retailers, Fiido don't show them on their website.
Bicycleland have an actual store in East London, and ARE approved Fiido sellers and bike fixers/servicers:
Electric Bike, Fiido eBike, ADO Bike, HIMO Z20 Electric Bike UK (bicycleland.co.uk)
Be aware, there is a T1 Lite, and a also regular T1 with a strengthened frame. AFAIK, both T1s have a 750w motor, which isn't UK street legal (if that matters to you).
RadPower also do a range of Cargo/Utility bikes that may also suit your needs:
Electric Cargo Bikes | Ecargo Bikes I Delivery Ebikes (radpowerbikes.co.uk)
Rad also have places in London where you can test-ride, and have your bike fixed/serviced.