Metlen, the Greek energy and metals group, led gains on the FTSE 100 after Greece was reclassified as a developed market by both FTSE Russell and index provider Stoxx, effective September 22. The upgrade elevated Greece from "advanced emerging" to "developed" status, reflecting continued progress in the country's recovery from its sovereign debt crisis.

Metlen, which moved its primary listing from Athens to London last year while maintaining a secondary listing in Greece, saw its London shares rise €3.38 or 7.6 percent to €47.50. This reclassification also enabled Metlen to join the pan-European Stoxx Europe 600 index, further increasing its visibility among investors.

Copper miners experienced strong demand amid rising metal prices, which climbed for a fifth straight session, nearing record highs around $14,875 per ton reached earlier in the month. Chilean miner Antofagasta advanced 116 pence (3.2 percent) to £37.73, and Anglo American increased 114 pence (2.9 percent) to £40.69.

In contrast, a decline in crude oil prices negatively affected energy stocks. Newly promoted blue-chip company Ithaca Energy was the biggest decliner on its first day in the FTSE 100, falling 12¼ pence (4.1 percent) to 284 pence. BP shares decreased 15¾ pence (2.8 percent) to 543 pence, while Shell dropped 50½ pence (1.4 percent) to £34.89. Meanwhile, British Airways owner IAG gained 13 pence (3.1 percent), buoyed by the prospect of cheaper jet fuel.

The FTSE 250 also saw notable performers, with Raspberry Pi among the top gainers. Its shares rose 46 pence (8.4 percent) to 593 pence amidst a broader global rally in stocks linked to artificial intelligence (AI). This rally followed a recent sell-off triggered by concerns about the technology’s potential risks, highlighting renewed investor confidence in AI-related firms.

Shareholders of Ferrexpo, a miner and commodities trader, overwhelmingly approved a $100 million equity raise earlier this month that allowed its shares to resume trading. Its stock closed up ½ pence (1.4 percent) at 284 pence.

Across the Atlantic, U.S. stock markets enjoyed gains driven by the AI sector and lower energy prices. The tech-focused Nasdaq Composite rose 2.3 percent to 27,122.09, while the S&P 500 gained 1.5 percent to 7,764.70. The Dow Jones Industrial Average increased 0.7 percent to 52,048.83. Chipmaker Advanced Micro Devices saw its market value surpass $1 trillion for the first time amid the upbeat sentiment.