The excitement of a new store never wears off,' says Ryan McDonnell, chief executive of Lidl UK – which is fortunate, because the German-owned discounter has opened its 1,000th British outlet just in time for the Christmas rush.

The cold Sussex drizzle in East Grinstead on opening day did little to deter customers. Shoppers streamed in, eyeing up festive food and toys. One sign of the cost-of-living crunch, McDonnell notes, is that people are starting their festive shopping earlier than ever.

'It's to spread the bill,' he says. 'We're selling our wooden toys in October and November. With confectionery, mince pies, and even wrapping paper, sales start earlier every year. Black Friday has almost become the whole month of November.'

This year Lidl is stocking 150 new seasonal lines, including Deluxe Violet Creams at £1.99 for 90g – a fraction of the price of the posh version from Fortnum & Mason. There's also a Dubai Chocolate Flavour Cream Liqueur – think Baileys on steroids – at £8.99 for 50cl.

Lidl boasts it can supply Christmas dinner for eight, turkey included, for £11.85.

McDonnell and his wife will be doing their own festive food shop in-store. 'We have champagne at £9.99 all through December, so I'll be picking up a few bottles,' he says, referring to the Comte de Senneval Brut champagne, reduced from £13.99. The bubbly in question has been flying off the shelves but Lidl hopes to replenish supplies this week.

McDonnell's personal favourite is the £9.99 Winter Wonderland Cheesecake. He says: 'Chocolate ganache, cream caramel on a digestive base with a hand-finished Belgian chocolate winter village scene – it's like a work of art. I'll eat all that and then fall asleep.'

Lidl may feel like a long-established fixture, but it has grown at breakneck speed since opening its first UK store three decades ago.

Owned by Schwarz Group, a privately held German giant, it has been the fastest-growing bricks-and-mortar retailer in Britain for more than two years. Profits more than tripled to £156.8 million in the year to February.

Can the expansion continue at this clip? McDonnell is emphatic that it can, pointing out that 25 more stores after the one in East Grinstead are scheduled to open by February next year. Would he like to open another thousand?

He says: 'It's hard to put a number on it. We'll open as many stores as the market allows. Every county, town and city probably has space for at least one more Lidl. We are nowhere near saturation.'

The stores follow a template designed for efficiency, but also to push healthier eating, with fresh fruit and veg at the entrance, though for treats the bakery is also close by. He says: 'We're selling four croissants every second.'

Lidl has also broadened its range, and set targets for sales of plant-based protein.

'We've worked really hard on adding more lines to make it more British, more relevant,' he adds.

With expansion, however, comes scrutiny, and Lidl is keen to burnish its UK credentials.

It has just published its first socio-economic impact report outlining its contribution to the country: 35,000 employees, £14.5 billion of economic value created this year, and nearly £700 million paid directly in taxes.

Investment in stores and distribution centres reached nearly £500 million, making Lidl one of the largest overseas investors in Britain.

McDonnell says: 'We think there are many years of expansion ahead. It's positive for the economy. It creates employment and it's good news for suppliers because we'll be selling more British food.'

He accepts that Tesco and Sainsbury's are the only big UK supermarkets obliged to publish frequent and full updates on their performance, being publicly listed on the stock market.

Asda and Morrisons are owned by private equity, and Aldi, like Lidl, has a privately-owned German parent. McDonnell says: 'Because we're privately owned, we don't have to publish accounts the way a listed business would.

'So our report is about transparency. It's helpful for our expansion to say, 'This is what we bring to communities.' We're a big employer and we want to show that we are growing responsibly.' McDonnell, 48, grew up in Dublin and is the first non-German to run Lidl UK. He studied German and Business at University College Dublin and has spent most of his career with Lidl, including stints in Germany and Austria. He took over as boss in 2022.

How independent is the UK arm?

'A lot of systems, structures and planning around infrastructure, finance and investment run through our main organisation,' he says. 'But in the UK we curate our range locally. We bring the brand to life in a distinctively British way. We're a British retailer, a British discounter.'

But being part of an international network helps in offering good value and also helps British suppliers, he says, adding: 'We are in a great position to export large volumes of British produce – whisky, salmon, cheese – into 30 markets. It's great for suppliers.'

He won't be drawn on the Budget or the wider economy, simply saying: 'There are always going to be economic headwinds. Our business model is built to be efficient and manage costs.'

But he has warned that the tax and National Insurance changes announced by Rachel Reeves in her first Budget would cost Lidl 'tens of millions of pounds'.

Lidl has also been vocal in backing farmers in their fight against inheritance tax – alongside Aldi and Tesco – in its role as one of Britain's largest supporters of domestic agriculture.

'We source around two-thirds of our products from British suppliers. Over five years we are committed to invest £30 billion into British food and farming. I must be one of the biggest investors in British food and drink,' he says.

It is all a far cry from Lidl's early 1990s image as a bare-bones discounter. McDonnell says: 'Our range has come on massively since we first arrived in the UK.'

So who shops at Lidl now? McDonnell smiles: 'Everybody comes to Lidl.'