Yep I know what are you saying and for a little difference I would pay the extra for ZEN.

But it was £35 -> £14, I can afford to not have a static for that difference.

For Sky superfast I only see £26/month with minimum 18 month term rising to £32/month thereafter and a £20 initial setup
so I assume the £14 must be a special offer, voucher code or switching site.

Yes they rung and offered me it for £14 for 18 months, I already had TV.

That will be why - with TV their internal costs for each additional subscriber will be far from linear so they can afford to subsidise deals even if close to wholesale rates.

Does the £14 include telephone (line rental) like the Zen fixed price does?

Yep it was to good to turn down. Includes line rental, I get full 80/20 sync and even includes unlimited calls.