Welcome to the Inspecs Group plc interim results to the end of June 2024. I am Richard Peck, Group CEO, and I'm joined by Chris Kay, Group CFO. I'd like to start with a summary of our activities in the period. As previously guided, revenue for H1 2024 decreased by 7.3% to GBP 103 million. We delivered operational efficiencies in the period, including the successful integration of our subsidiaries in the USA. Strong cash generation in the period, including working capital reduction, allowing the continued reduction in net debt. Our new Vietnam manufacturing facility completed on time and on budget. Distribution was agreed for new brands into leading retailers. Trading in the second half of the year is ahead of the prior year, and our order books are also ahead.
I'll now hand over to Chris to take you through the numbers.
Thank you, Richard. Richard's already explained about the headline operating revenue. I'd like to just say that with constant currency basis, the pound did strengthen during the year against the dollar, and as a result, the difference from H1 2024 to H1 2023 was slightly less. We worked hard on our operational efficiencies, with our operating expenses reducing from GBP 52.6 million to GBP 50.7 million. Looking at the underlying EBITDA, this dropped from GBP 12.1 million to GBP 10.1 million. On a constant currency basis, that would have been an H1 2024 performance of GBP 10.4 million. Our cash generation was exceedingly good during the first half of 2024, and that was helped in particular by inflows from working capital of some GBP 2.4 million.
Finally, our gross profit margin moved up again, another 100 basis points from 51.4% to 52.4%, and the guidance going forward is for that gross profit margin to remain at that level in the second half. Finally, our net debt reduced by GBP 4.4 million, from GBP 24.2 million to GBP 19.8 million. And I'll come to a more detailed explanation on that debt movement in a later slide. Coming to the group income statement, I'd just like to pick out the depreciation and amortization, which is starting to reduce on a six-month basis from 6.6 to 6.2. And on the earn-out from acquisitions, we have one final earn-out to pay in March of 2025, and that completes all future earn-outs based on all acquisitions to date.
If I may now turn to the underlying EBITDA bridge, again, this has moved from 12.1 to 10.1, and the main movements is in relation to our frames and optics segment, which had a decrease in gross profit due to a volume decrease of 2.9, and it had a decrease in operating expenses of 0.9. Our other segments, manufacturing, lenses, were relatively flat. Moving on to working capital, we had a strong reduction in net debt of some 18%. We had strong cash generation during the period. As a result, we were able to reduce our leverage down to 1.63.
Looking at guidance for the future, we are estimating that our leverage at the end of the year, that's December 2024, should be around a single-digit number, and our debt service cover headroom will increase significantly. At this point in the cycle, at the 30th of June 2024, we look back 12 months to calculate that number, and that therefore includes the CapEx, which was quite significant on the new Vietnam facility. And finally, we see our interest rate ratio cover increasing in the second half, with a reduction of interest on our outstanding loans. If I may now move to the net debt, excluding leases bridge. So our net debt started the period at GBP 24.2 million. We had an inflow of GBP 9.6 million from operating expenses, and then another inflow from working capital of some GBP 2.4 million.
The guidance for the second half is that we'll probably be flat on our working capital, and during our cycle, we do increase the level of inventory towards the end of the year. Interest charge was some GBP 1.8 million, and we expect that to reduce in the second half, and then accelerate the reduction in 2025. Finally, we invested GBP 2.6 million during the period in our factories build out in Vietnam, and also on some earn-out on acquisitions. Finally, we repaid GBP 1.8 million of our lease debt. This gave a final figure for the period of GBP 19.8 million, and we're expecting that to reduce further to around GBP 16 million at the end of the year.
Finally, on the group cash flows, as I've said, we had an inflow of GBP 2.4 million. We expect that to be relatively flat in the second half, and overall, the group expects in the second half to be able to start reducing debt on its RCF facilities. But now hand back to Richard to look at the operational highlights.
Thank you, Chris. Our operational highlights for the period I will cover in our segmental analysis, but it includes brands, our new factory in Vietnam, our research and development work, our supply chain work, our group integration work, and the development of our factory, our Norville factory in Gloucester. Starting with the frame and lens segment, which is our biggest segment, and this covers optical frames, sunglasses, and our magnifier business. As you can see, we had a small decrease in revenue in the period, primarily driven by a slowdown in key accounts in Northern Europe. We launched a key brand with a major global retailer in all stores. We launched additional brands with two major retail chains in the United States.
We increased our travel retail business by 45%, and we successfully integrated Inspecs USA and Tura, our frame businesses in the United States. You will also see that our gross profit in the period increased to 51.8%. Moving on to manufacturing, this covers our Killine business in Asia. A very busy period for them. Although sales in the period were very slightly down on last year, they have now recovered. We've seen an increased gross profit margin. We've built a wonderful new facility, which increases our capacity in Vietnam significantly, and we've seen increased sales in our Italian manufacturing site, Cadore, where we manufacture our rolled gold Savile Row Eyewear. Lastly, our important lens business.
We achieved 21% growth in the period both from new key accounts and independent sales channels. We signed a significant new key account, and we are negotiating other new key accounts. None of these are in these numbers. Our leadership team is now well embedded, and Norville has been instrumental in assisting our R&D department in the development of smart eyewear. Lastly, turning to our current trading and outlook. As of the thirty-first of August, H2 trading to date exceeds the prior year, and our order books are also 7% ahead. We are commencing the distribution of key brands into major retail chains across the USA and Canada in H2. We will be launching a new Eschenbach Optik low vision aid called Optaro, which is a mobile phone magnifier.
We are delivering operational efficiencies, with further work in progress on the amalgamation of our supply chain via both internal and third-party manufacturing. As I've already said, we've built a wonderful new manufacturing facility in Vietnam, which significantly increases our capacity and capabilities. We continue to reduce our net debt, which will increase at an accelerated pace in H2. And whilst we remain cautious in relation to market conditions, the board is confident in meeting market expectations for the full year. Thank you.