If I take my NOW TV Box to Spain will I be able to access iPlayer on my television (obviously my television is connected to my wifi)?
Appreciate the knowledge of those of you out there.

Not without a VPN or SmartDNS installed in your router or it will be blocked as it cannot be used (officially) outside the UK.

Very few routers will allow you to install a VPN but installing a SmartDNS is easy in most routers. SmartyDNS costs about €35 a year and works fine.

Many devices, TVs, iPads, etc will allow you to change the DNS settings in the actual device, but the NowTV box is the exception to this.

The NowTV box is an excellent device as it gives all the UK catchup services and also live TV from BBC and ITV. It only costs £15 including postage in the UK and a HDMI cable.

I recommend Overplay.net for SmartDNS. Good service and it's possible to appear to be in different countries for different services. For example, you can set it to the UK for iPlayer and NowTV, and the US for Netflix. Handy. It's takes about 30 seconds to setup the router.

Thanks to both of you for that. I will look into the Smart dns when I'm next out in Spain as they appear to offer a free trial.

Here are some frequently asked Qs about SmartDNS

https://www.cactusvpn.com/support/faq-smart-dns/#q4