The FTSE 100 fell into negative territory on news that US tariffs will be applied on aluminium and steel imports from the European Union, Canada and Mexico.

The blue-chip index advanced 1.8 points to 7,691.

In the US, the impact was more deeply felt as investors were worried about potential retaliatory measures. The Dow Jones declined 0.8% to 24,459 around 4:45pm UK time.

Brent crude oil nudged 0.6% higher to $78 per barrel.

MID AND LARGE CAP RISERS AND FALLERS

Transport operator FirstGroup (FGP) reversed 18.9% to 89.8p after racking up £326.9m of pre-tax losses in the year to 31 March and announcing the resignation of chief executive Tim O'Toole.

Building materials specialist CRH (CRH) revealed several business improvement initiatives, helping the shares strengthen 3.2% to £27.65.

Chemicals company Johnson Matthey (JMAT) rose 3.4% to £35.13 following a 2% increase in pre-tax profit and a 17% jump in sales in the year to 31 March.

Shares in events firm UBM (UBM) were lifted 2.9% to £10.28 following the UK Competition and Markets Authority's announcement it will not be investigating its proposed acquisition of Informa (INF).

Greetings cards seller Card Factory (CARD) said like-for-like sales dipped 0.4% in the quarter to 30 April in a tough retail environment. Its shares dropped 9.2% to 198.3p.

Premier Oil (PMO) announced it will be joining the FTSE 250 from 18 June, prompting investors to mark the shares 7.6% higher to 119.9p.

SMALL CAP RISERS AND FALLERS

Ophir Energy (OPHR) said it was talking to potential partners about funding its Fortuna project after Schlumberger exited the OneLNG joint venture, which Ophir is in with Golar LNG Partners. Shares in Ophir dropped 10.8% to 56.3p.

Car retailer Caffyns (CFYN) fell 4.7% to 405p as challenging market conditions hit pre-tax profit, which fell from £2.1m to £1.4m in 2018.

Natural resources investing company Cluff Natural Resources (CLNR) slumped 24.8% to 2.7p despite the UK Oil and Gas Authority waiving its requirement for a farm-out deal to be finalised by 31 May on its two licenses.