According to Sheffield council -
http://www.sheffield.gov.uk/environment/how-we-work/bereavement/rules-and-regs copy
There are specific regulations, (which I presume will be quite similar per regional council) in terms of tombstone regulations.
Sheffield council regulations are as follows -
"MARKER STONES
On all graves where an Exclusive Right of Burial has been granted, a stone tablet of approved design, not exceeding 300 mm x 150 mm in surface section and not less than 50 mm thick, shall be permitted. The stone shall be laid flat with its upper surface below the surrounding turf level. Only the surname of the deceased and the grave number and section may be engraved on the stone, except for Woodland Burial marker stones which state deceased, year of birth and death and grave number and section."
Newbury council mentions teh following -
"Monuments and Inscriptions to be approved. No monument shall exceed 3ft, 6ins in height. A person shall not erect or fix any monument or gravestone, tablet, or make any inscription thereon, or place therein any vase bearing an inscription in the Burial Ground, without the approval of the Council and shall, before proceeding to erect or fix any such monument, gravestone, tablet or make any inscription thereon, or place any such vase bearing an inscription, furnish to the Council a description and measurements of every such monument, gravestone, tablet, vase, kerb or railing, with copies of the proposed inscription thereon, together with a specification of the material and dimensions to be used. All installations must be in accordance with current NAMM recommendations.
The Council will remove any unauthorised memorials, kerbs, railings, ornamentation or horticultural decoration. The Council may recover the cost of removal of these items from the holder of The Grant of Exclusive Right of Burial to that grave, in accordance with the powers and procedures set out in Article 14 of The Local Authorities Cemeteries Order 1977."
source - http://www.newbury.gov.uk/cemetery5.htm copy
I suggest contacting your local council or visiting their online edition of rules and regs, and if the mason did not abide by these standards, its maybe an issue for trading standards?
Hope that helps..