Delegating requests for www and ftp

[Marco]

I want to name my LAN markhawkes.com, so all my computers will be

* ns.markhawkes.com      (192.168.100.2)
* neptune.markhawkes.com (192.168.100.5)
* jupiter.markhawkes.com (192.168.100.6)
* saturn.markhawkes.com  (192.168.100.7)
* etc...

However, when I request ftp.markhawkes.com or www.markhawkes.com
I'd like my DNS server to somehow delegate resolution of these
names to ns0.visn.co.uk, the nameserver that's authoritative for
markhawkes.com out there in the big wide world. Hence my internal
machines will be able to see the public versions of my web site
and ftp server that everyone else can reach.

Basically I want to share authority of markhawkes.com between 2
nameservers: my internal one, serving my LAN, and ns0.visn.co.uk,
which serves everyone else (and my LAN when they ask for www and
ftp).

Would the following zone file do what I want? What's the neatest
solution?

----- zone file for markhawkes.com -----
$ORIGIN markhawkes.com
@   IN   SOA   ns.markhawkes.com.   foo.markhawkes.com ( blah )
     IN   NS    ns.markhawkes.com.

; delegate www and ftp requests to ns0.visn.co.uk (?)
www.markhawkes.com.  IN  NS  ns0.visn.co.uk.
ftp.markhawkes.com.  IN  NS  ns0.visn.co.uk.

; I don't think I should declare an A record for this host
; because I'm not responsible for it. It belongs to my ISP:
ns0.visn.co.uk.      IN  A  195.149.39.184

; my internal hosts
ns       IN  A  192.168.100.2
neptune  IN  A  192.168.100.5
jupiter  IN  A  192.168.100.6
saturn   IN  A  192.168.100.7
-----

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