CELTIC last night strengthened their squad and weakened their League Cup final opponents in the process by signing Stuart Armstrong and Gary Mackay-Steven from Dundee United in the final hours of the transfer window.

On a busy deadline day throughout Scotland, persistence was the key, with Celtic having several bids for Armstrong turned down before United finally accepted an offer thought to be in the region of £1.7m. The 22 year-old midfielder has signed a three-and-a-half year deal. "It's a lot to take in," he said. "I'm delighted to be here and delighted to have signed on at such a massive club."

Mackay-Steven had already signed a pre-contract agreement to move to Celtic Park in the summer but manager Ronny Deila had been keen to recruit the winger this month if possible and that move materialised late on with the 24 year-old completing a four-and-a-half year-deal. The move bolsters Deila's options with Celtic still involved in four competitions heading into the last three months of the season, including the League Cup where they will meet a now-weakened United in the final on March 15.

United moved quickly to try to fill the void by attempting to bring back Scott Allan from Hibernian, but were thwarted in their attempts after having multiple bids rejected. Hibs, in fact, added to their midfield options by recruiting Fraser Fyvie until the end of the season but couldn't complete a loan move for Celtic's Liam Henderson. United did get one former player to return, full-back Paul Dixon moving back to Tannadice after being released by Huddersfield Town.

Celtic rounded off a productive day by finalising a deal for Michael Duffy, the Derry City forward, who had spent two spells on trial at Lennoxtown. The 20 year-old is a Northern Ireland under-21 international.

Proposed moves for Robbie Muirhead, the young Kilmarnock forward, and Zakaria Bakkali of PSV Eindhoven failed to come to fruition. Instead United were trying to confirm a deal for Muirhead as the window closed, some comfort for manager Jackie McNamara on an otherwise frustrating day.

Leaving Celtic was Filip Twardzik, the midfielder joining Neil Lennon at Bolton Wanderers after completing a two-and-a-half year deal. Lennon, though, would fail in his attempt to also recruit Kris Commons, with contract talks between the midfielder and Celtic now expected to resume in the coming weeks. Eoghan O'Connell, the 19 year-old defender, committed his long-term future to the club by signing a two-year contract extension.

Across the city, there was further evidence of Mike Ashley's growing influence at Ibrox as Rangers recruited five fringe players on loan from Newcastle United in an attempt to bolster their promotion prospects. Haris Vuckic, Remie Streete, Kevin Mbabu, Gael Bigirimana and Shane Ferguson all signed on until the end of the season, although it is thought manager Kenny McDowall wasn't consulted prior to their recruitment.

Vuckic is a Slovenian midfielder with one international cap, Streete is a 20 year-old central defender who previously had a loan spell with Port Vale, Mbabu is a former Swiss under-19 defender, Northern Irish international Ferguson plays on the left side either at full-back or midfield, while Bigirimana is a former England under-20 midfielder who has not played for the Newcastle first-team since August 2013.

"Pleased to have joined @RangersFC on loan until the end of the season. Looking forward to coming to Glasgow," tweeted Streete.

Away from the Old Firm, the two most significant transfers on the final day of the window involved Tony Andreu, who left Hamilton Academical for Norwich City for around £1m, while Kenny McLean departed St Mirren for Aberdeen for around £275,000.