Factbox: What changes does Britain want to N. Ireland post-Brexit rules?

LONDON (Reuters) - Britain is demanding the European Union agree to rework the post-Brexit trade rules governing trade with Northern Ireland, seeking more time, better solutions and, in some cases, a renegotiation of the existing deal.

To avoid creating a hard border on the island of Ireland, Britain agreed to a deal in which Northern Ireland remained within the EU's single market. This has instead created a regulatory border between Northern Ireland and the rest of the United Kingdom.

Since leaving the EU at the end of 2020, serious problems with implementing the exit deal have come to light, even before grace periods waiving some of the new regulations has expired.

Britain's demands, set out in a letter last week, are due to be discussed with the EU on Thursday. They are:

SUPERMARKETS - Extend waivers on certification requirements from supermarkets and their suppliers to at least Jan. 1 2023, from April 2021 currently. The government also wants this scheme to be open to more businesses.

CHILLED MEATS - Extend the free transport of certain types of chilled meats until Jan. 1 2023, from June 30 2021 currently. Without a waiver, legal restrictions prohibit the movement of goods such as sausages.

PARCELS - Extend a waiver on customs declarations on mail parcels sent from the rest of the United Kingdom to Northern Ireland until at least Jan. 1 2023 from March 31. 2021 currently.

MEDICINES - Extend the free movement of medicines between Northern Ireland and the rest of the United Kingdom until at least Jan. 1 2023 from Dec. 31 2021 currently.

SEED POTATOES - The renegotiation of arrangements preventing the movement of seed potatoes, other plants and plant products.

STEEL - A solution that provides tariff-free movement of steel between Britain and Northern Ireland. An anomaly in the way tariffs and quotas are applied by Britain and the EU has raised the prospect of a 25% tariffs on steel moving to Northern Ireland.

PET TRAVEL - A bilateral arrangement with Ireland to remove barriers to owners taking their pets into Northern Ireland and Ireland from the rest of the United Kingdom.

The government said this list of demands was not exhaustive.

(Reporting by William James; Editing by Gareth Jones)