Keeping my landline number when I leave Virgin Media and transfer to another Internet Service Provider (eg Sky)

I've been overpaying Virgin Media massively for the past couple of years and finally intend to transfer to another ISP, eg Sky, as soon as possible.

I've had my landline number for many years and wish to keep it when I transfer ISP.

I've heard that the process to keep a landline number is slightly different when transferring from a cable ISP like Virgin Media to a non-cable ISP.

I'd be really grateful for any advice about the process of porting / transferring a landline number from Virgin Media to another ISP.

And while I'm here, if you have any recommendations for a good ISP, that'd be fantastic - thanks a lot in advance!