UKC

I've always worn Wigwam hiking socks as they have no seam in the toe box, but Wigwam are pretty much impossible to get in the UK now. Does anyone have a good alternative?

Synthetic or merino, lightweight or midweight.

Thanks!

Have a look at Darn Tough Socks. 

Yes, I second this. 

This summer I walked the TMB in just 2 pairs, washing a pair each night. Not a single blister was had in 10 days and they are super comfy. 

I've used 1000mile socks in many ultras. They are double layer, so reduce friction. But they have a seam at the end.

Injinji toe socks dont have a seam. Again I've used them in ultras. They are great, but can be a faff to put on.

Bridgedale are my default 

As mentioned ininji are good toe socks. I found thousand mile socks too narrow and not very stretchy. Dubarry fell apart quickly. 

I have been eyeing up some Nordic socks but not purchased any yet

Mine too; Trail, in particular (picked up lots in TK Maxx in the last couple of years, to add to my much older ones). They have proves very durable.

There is a toe box seam, but it is flatlocked, and I have never noticed it in wear.