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The size you quote for the aperture is extremely small for modern hobs.
Even the smallest Hotpoint hob requires 555mm wide by 475mm deep.
Click here for the Hotpoint hobs
The cut out sizes are shown at the bottom of each hob specification.
Click here for Bosch hobs
You have to click on the hob and then on technical specs tab to see the cut out required for the hob.
Click here for Candy Hobs
Again, click on the hob and you'll get the cut out required.
Click here for AEG hobs
Click on the Gas Hobs tab then on the Gas hob link you want to see.
You should get the cut out information there in the product specs.
There's also a brochure, click here for the brochure
If you can gain an extra 5mm on the cut out on your worktop, it gives you a wide choice of hob.
At the sizes you've posted, there are very few hobs that will fit.
Check them out, see what you find and get back to me if you need more help.
Whilst there are strict regulations on gas appliances the same doesn't apply to electric hobs.
Your existing hob would have had a clearance figure in the original installation instructions.
The figures you've quoted above would mean that a gas hob installed would contravene the regulations (and possibly void your house insurance).
You will likely find you still need the extra 5 mm on the space the hob fits into.
The overall size on top of the worktop would be 580mm wide and 51mm deep.
This should compare favorable to the existing hob.
Check out the same links as before but select electric appliances.
You're very welcome.
Good luck with the new appliance.
Hope this helped