I've just switched to iD from Lebara (Vodafone).
Unfortunately my data speeds indoors and outdoors at CW13PL are very poor, mostly hovering around 1mb download, though uploads are mostly unaffected. My signal strength is high and I can connect easily to both 4G and 5G, so I suspect a data bandwidth issue.
I've reset my network settings, checked the coverage map for any issues and restarted my phone but to no avail. I'm using a Pixel 6 and the iD phone number is on the eSIM.
If there is no improvement I'll be dipping out before the 14 days cooling off period ends as those speeds are just absurd.