Thank you for your reply Kain.
The number on my primary line, that I would wish to change, was previously used for some business work but notwithstanding is also plagued with nuisance/unsolicited calls. I am very keen to get rid of it and only wish to pay for one landline on my already significant Virgin package. The number on my "additional line" is that which is mainly used for friends, family, etc and therefore the one I would wish to somehow retain please.
I was informed by customer service that it is possible to change a number on an existing line and wondered if it would therefore be possible to cancel my additional line, free up that number, and then transfer/change that number to my primary/remaining line?
Having to cancel all my landlines and start again with an all new number seems a bit drastic. In that case it may be easier to forget about a landline package altogether and just use mobiles.