Well, what you called a "shift of England (between EIA and LIA) towards Germanics" also looks like a "shift of England (between EIA and LIA) towards Scotland_IA" to me. So this admixture could be from northern parts of Britain, rather than from areas across the North Sea. Another issue - you should check the regional distribution of England_EIA, England_MIA and England_LIA samples. Because for example if England_EIA samples are mainly from South England; England_MIA samples mainly from English Midlands; and England_LIA mainly from Northern England - then this observed "shift" is not a shift at all, but just a function of geography (because already in the Early Iron Age there was more of EEF admixture in the south of Britain than in the north).
The next thing:
What about uniparentals? If you are unsure about something based on auDNA, maybe a good idea is to check haplogroups?
Maciamo calculated haplogroup statistics and posted on his Eupedia Forum, I'm quoting him:
https://www.eupedia.com/forum/thread...l=1#post636856
Early Iron Age Britain (n=14)
I2a2-M223>Y3259>Y6098>PF692
R1b-P297
R1b-M269
R1b-L52
R1b-U106>S264
R1b-P312
R1b-P312
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251>A11676
R1b-P312>L21>DF13>DF21
R1b-P312>L21>DF13>DF49>DF23
R1b-P312>DF27>Z195>Z29704>S11475
Middle & Late Iron Age Britain (n=146)
F
F
F
F
G2a-L497>Z1815>Z1816>BY27899
G2a-L497>Z1815>Z1816>Z1823
G2a-L497>Z1815>Z1816>Z1823
G2a-L497>Z1815>Z1816>Z1823>Z726>S23438
G2a-L497>Z1815>Z1816>Z1823>Z726>Z16775
I1
I2a1a-M26>L160
I2a1a-M26>L160>Z105
I2a2a-M223>Y3259>Y6098
I2a2a-M223>Z284>L1195
I2a2a-M223>Z284>L1195
I2a2a-M223>Z284>L1195>Y3684
I2a2a-M223>Z284>L1195>Y3684
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269
R1b-M269>PF7562>Y83965
R1b-L52
R1b-L52
R1b-L52
R1b-L52>L151
R1b-L52>L151
R1b-L52>L151>S1200
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312
R1b-L52>L151>P312>S461
R1b-L52>L151>P312>Z30597
R1b-L52>L151>P312>Z30597
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13
R1b-P312>L21>DF13>A1101
R1b-P312>L21>DF13>CTS1751>FGC49766
R1b-P312>L21>DF13>DF1
R1b-P312>L21>DF13>DF1>S5668
R1b-P312>L21>DF13>DF21
R1b-P312>L21>DF13>DF21
R1b-P312>L21>DF13>DF21>BY11117
R1b-P312>L21>DF13>DF21>DF25>DF5
R1b-P312>L21>DF13>DF21>DF25>Y12651
R1b-P312>L21>DF13>DF21>S5488
R1b-P312>L21>DF13>DF21>S5488
R1b-P312>L21>DF13>DF21>S5488
R1b-P312>L21>DF13>DF21>Y2890
R1b-P312>L21>DF13>DF49
R1b-P312>L21>DF13>DF49
R1b-P312>L21>DF13>DF49
R1b-P312>L21>DF13>DF49
R1b-P312>L21>DF13>DF49>DF23
R1b-P312>L21>DF13>DF49>DF23>Z2961
R1b-P312>L21>DF13>DF49>BY23924
R1b-P312>L21>DF13>FGC5494
R1b-P312>L21>DF13>FGC5494>S1088
R1b-P312>L21>DF13>FGC5494>S1088
R1b-P312>L21>DF13>FGC5494>S7958>BY33481
R1b-P312>L21>DF13>FGC5494>Y31855
R1b-P312>L21>DF13>S1026>BY173541
R1b-P312>L21>DF13>S1026>Z16887
R1b-P312>L21>DF13>S1051>FGC19428
R1b-P312>L21>DF13>Y14049>BY9003
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251
R1b-P312>L21>DF13>Z251>Y11273
R1b-P312>L21>DF13>Z253
R1b-P312>L21>DF13>Z253
R1b-P312>L21>DF13>Z253
R1b-P312>L21>DF13>Z253>Z2185
R1b-P312>L21>DF13>Z253>Z2185>Z2186
R1b-P312>L21>DF13>Z253>Z2534
R1b-P312>L21>DF13>Z253>Z2534>A14
R1b-P312>L21>DF13>Z253>Z2534>BY13089
R1b-P312>L21>DF13>Z255>Z16436
R1b-P312>L21>DF63
R1b-P312>L21>DF63
R1b-P312>L21>DF63
R1b-P312>L21>DF63
R1b-P312>L21>DF63
R1b-P312>L21>DF63
R1b-P312>L21>DF63>CTS6919
R1b-P312>L21>DF63>FGC36421
R1b-P312>L238>Z2245
R1b-P312>DF27
R1b-P312>DF27>FT318890>Y3267
R1b-P312>DF27>Y14529
R1b-P312>DF27>Y30754
R1b-P312>DF27>Y30754>Y85515
R1b-P312>DF27>Z195>Z262
R1b-P312>DF27>Z225>Y89302
R1b-P312>DF27>Z2572
R1b-P312>U152>L2
R1b-P312>U152>L2
R1b-P312>U152>L2>Y3961>Y17997
R1b-P312>U152>L2>Z49>Z142>S7402
R1b-P312>U152>L2>Z49>Z142>S7402>FGC12384
R1b-P312>U152>L2>Z49>Z142>Z51>Z57>Z53
Haplogroup frequency:
R1b = 88.3% (including 58.2% of L21, 6.8% of M269, 5.5% of DF27, 4.1% of L2 and 0% of U106)
G2a-L497 = 3.4%
I2a2a-M223 = 3.4%
F = 2.7%
I2a1a-M26 = 1.4%
I1 = 0.7%
=====
In other words, ABSOLUTE LACK of Germanic Y-DNA haplogroups in Iron Age Britain, except for maybe one singleton I1.
What percentage of English males today carry Germanic Y-DNA ??? I don't remember exactly, but surely double-digits.
And in IA England it was no more than 1% (if that singleton I1 is real - and not misdated or a wrongly assigned haplo).
To sum up, there was no male-mediated Germanic admixture in Iron Age England. Maybe female-mediated.
Maybe Britons were buying blond-haired Germanic slave girls and got Germanic admixture - if you want to believe this.