The company revealed that it opened 16% of its estate for outdoor trading only on 12 April building to 44% by 16 May as restrictions eased across Scotland and Wales.
During these initial five weeks like-for-like sales compared to 2019 were at 63% of pre-Covid levels.
However, it revealed that since reopening substantially all of its estate on 17 May that the 10 weeks of trading both indoors and outdoors have seen volatile sales.
In the first five weeks like-for-like sales were strong at 98% of pre-Covid levels, supported in particular by pent up consumer demand on full re-opening, it said.
Across the following five weeks activity was slower on average, with like-for-like sales at 89% of pre-Covid levels.
It said that recently there has been some sign of improvement following further easing of restrictions on "Freedom Day" in England.
Sales strong in suburban sites
Aside from the impact of selected games during the Euros, sales have generally been stronger in suburban and food-led brands, with city centre sites being the most challenged.
Total sales year to date, including 18 weeks of enforced closure are at 35% of pre-Covid levels.
Phil Urban, chief executive, said: "The continuing uncertainty relating to the pandemic still makes forward guidance difficult, and is likely to do so at least until into the Autumn.
"However with our diversified portfolio of well-known brands and largely freehold estate, and our continued focus on efficiency though our Ignite programme, supported by a strengthened balance sheet, we are in a strong position coming out of the pandemic as restrictions ease further."
The company said it has now signed a relationship agreement with its major shareholder, Odyzean Ltd.