The "Newry Effect" refers to the fact that households in the Republic of Ireland went shopping in Northern Ireland $($part of the United Kingdom$)$ because:

the stores in Newry accepted payments in euros.

the households were more familiar with British brands than they were with European brands.

the value of the euro had appreciated against the British pound.

sales taxes $($VAT$)$ were lower in the UK than in Ireland.

there were more choices available in shops.