Watch List notes:

(g) Victoria (1837-1901), 'Shieldback' Sovereigns, 1870, Type IB (2), [Die 86], second larger young head, W.W. raised on truncation, rev. crowned normal shield in wreath, edge milled, 7.99g, 6h (Bentley 215); another, similar, [Die 86], 7.97g, 7h (MCE 530; Marsh 54; Bentley 216; Spink 3853B), a remarkable pairing from the same obverse and reverse dies as denoted by the die number and flaw emanating from the crown of the 1 in date, the first scratched and lightly cleaned, otherwise both residually lustrous, a bolder very fine (2).
Clearly these two were struck at different periods of the same journey given the expansion of the obverse flaw between the first and second coin. Unsurprisingly the aggravation of repeated striking blows has also caused the reverse die to begin rotating on its axis during production - again a subtle feature testified between the two coins.
Estimate: £800 - £1000