It is not the thickness that is a problem, it is the length of the slot.
I buy "Thick White Toastie" loaves from Lidl. The length is far too long to go in sideways into the toaster, so it sticks out about 1/3 when put in the other way around.
What is totally beyond me is why toasters are made that won't actually toast standard size bread.
Is it the EU, I wonder, with their rules about vacuum cleaners that don't suck, kettles that take ages to boil, etc? So probably toasters that don't toast as well :mysmilie_10: