Timing inspection hole bung stuck fast

Hello,
Does anyone have any bright ideas on how to remove the stuck fast timing inspection hole bung without rounding off - must be a common problem.
Cheers
Book.

Common problem , not trying to teach you to suck eggs but you do realise the correct removal method is with a massive allen key or bolt head to fit and unscrew it , no idea of the size though ?

Yeah got the correct allen key its just stuck tight - maybe a series of extenders to increase the leverage and a tin of spinach - I've just never come across a nut so blimmin tight…
Nothing is ever simple with these grouchy, bad tempered, luck-less blinking soul destroying cars. Spleen vented.
Must be the challenge that keeps us keen.
back to it.
cheers
Book.