Indded the UK map seems unusual, it looks like the north part is more stretched than the south part of the map. Looking at your code, I see: projection=dict(type="equirectangular").

On Wikipedia page for this type of projection, they have this map which shows that the distorsion is not symmetric around UK as it is pretty far from the Equator:

On this website they say that

The map projection commonly used for Britain is the Ordnance Survey National Grid projection which is a Modified Transverse Mercator projection.

And on Plotly website they give a long list of map projection types that are available:

Code: fig.update_geos(projection_type=) Type: enumerated , one of ( "airy" | "aitoff" | "albers" | "albers usa" | "august" | "azimuthal equal area" | "azimuthal equidistant" | "baker" | "bertin1953" | "boggs" | "bonne" | "bottomley" | "bromley" | "collignon" | "conic conformal" | "conic equal area" | "conic equidistant" | "craig" | "craster" | "cylindrical equal area" | "cylindrical stereographic" | "eckert1" | "eckert2" | "eckert3" | "eckert4" | "eckert5" | "eckert6" | "eisenlohr" | "equal earth" | "equirectangular" | "fahey" | "foucaut" | "foucaut sinusoidal" | "ginzburg4" | "ginzburg5" | "ginzburg6" | "ginzburg8" | "ginzburg9" | "gnomonic" | "gringorten" | "gringorten quincuncial" | "guyou" | "hammer" | "hill" | "homolosine" | "hufnagel" | "hyperelliptical" | "kavrayskiy7" | "lagrange" | "larrivee" | "laskowski" | "loximuthal" | "mercator" | "miller" | "mollweide" | "mt flat polar parabolic" | "mt flat polar quartic" | "mt flat polar sinusoidal" | "natural earth" | "natural earth1" | "natural earth2" | "nell hammer" | "nicolosi" | "orthographic" | "patterson" | "peirce quincuncial" | "polyconic" | "rectangular polyconic" | "robinson" | "satellite" | "sinu mollweide" | "sinusoidal" | "stereographic" | "times" | "transverse mercator" | "van der grinten" | "van der grinten2" | "van der grinten3" | "van der grinten4" | "wagner4" | "wagner6" | "wiechel" | "winkel tripel" | "winkel3" )

Ordnance Survey is not available but Mercator is and you can try several projections until you find one you prefer?