Pure British with high amounts of Southern European DNA? (Gedmatch MDLP results)

[thracian_bro]

When comparing the MDLP k23b mixed population results for two kits, both kits claiming to have ancestry exclusively from the British Isles, one of the kits had a significantly higher amount of Southern European DNA (well over 1/3 in some cases), being more similar to a Croat/Austrian/Slovene than Anglo. The other kit was almost entirely NW European. What could be the reason for this?

http://imgur.com/J1gMHwQ
http://imgur.com/R2ilqIl

[Leto]

The latter seems to be a pure British Islander.

[thracian_bro]

The latter seems to be a pure British Islander.

Is it common for British to have this level of variance in their heritage? Would any Brit with significant DNA outside of NW Europe, as shown here, be considered average?

[J. Ketch]

Is it common for British to have this level of variance in their heritage? Would any Brit with significant DNA outside of NW Europe, as shown here, be considered average?
No. British are relatively homogenous. Although I wouldn't judge on an MDLP calculator.

[thracian_bro]

No. British are relatively homogenous. Although I wouldn't judge on an MDLP calculator.

I thought MDLP was rather accurate in it's ancestry estimates. Eurogenes k13 being the best to use I assume? The variance shows much less there, I wonder why this is only visible with MDLP and some calcs like PuntDNAL. People of almost entirely NW ancestry seem to score overwhelmingly NW across all non-African calcs, so exceptions like this stuck out to me.