My question is can we renew while at address A in the hope that it will only be a small admin charge when we move to address B?

Highly unlikely, no more so than if the Astra was changed from 'cooking' version to top of range.

Postcode is a proxy for risk and can be counter-intuitive. My son lives in Liverpool in a flat conversion on a major thoroughfare (Aigburth Road) and quite close to Toxteth. Before that he was lodging with his girlfriends family in detached house on what I'd guess is an eighties/nineties development; a mix of semis and detached designs, all built for purchase, near Croxteth Park. His insurance (for a Pug 107) was considerably higher there than it is now - proximity to some less pleasant areas.

My suggestion would be to shop around. Not all insurers rate risk in same way.

Edited by Bromptonaut on 28/10/2019 at 08:12

Most insurance firms will charge about £25 (sometimes more) for a mid-year change in policy, which will likely negate any saving over that two week period. You have to make some legal arrangement at their normal home address, so I'd speak to your insurer to see what they can do and ask why the premium is so much higher.

To be honest, it's something on my list of things to check when I'm looking to move home, as significantly higher insurance can make a large impact on monthly/annual outgoings. You may want to check what your own premium may be rising to as well so you don't get another shock in a few months' time.

I would also check the details of your other address, especially the postcode to see whether it is correct. As Brompt says, sometimes moving not that far can make a large difference in premium due to the new one being a higher crime and/or higher risk (accidents - e.g. near to an accident blackspot [which you may not be aware of]) area.

I would also look at other insurers in case going via the first is an anomaly - you never know.