Middlesex started strongly when opener Artemis Downer, who hit an unbeaten 60 when they hammered Glamorgan by 10 wickets earlier in September, impressed with a couple of boundaries before being caught at point off Anna-Mae Shearn.

Izzy Routledge and Sproul helped steady the ship with a fluent 60-run partnership, before Routledge was caught at mid-off from a Nicole Reid delivery.

Sproul soon followed for a solid 43 from 67 balls when caught and bowled by Poppy Walker.

Poor Glamorgan fielding, with several dropped catches and a missed stumping, boosted Middlesex as Horley and Trussler put on 131 before the latter was stumped by Abbey Freeborn off the bowling of Eve Jackson.

Horley’s innings was ended on 117 but she helped Middlesex set a tough target of 279.

They got their breakthrough in the fifth over when influential captain Lauren Parfitt was bowled by Siya Nanavati for eight.

Glamorgan’s woes continued when the hard-hitting Daisy Jeanes was caught at mid-wicket off Issy Routledge.

The wickets continued to tumble when Horley followed up her century by taking the wickets of Bethan Ellis and Megan Sturge as Glamorgan slumped to 72-4.

A 72-run partnership between Freeborn and Gammon offered some hope, until the former was bowled by Anaya Patel for 43.

Glamorgan won the League Two T20 Blast but Hannah Davis extinguished any hopes of a double with two swift wickets, including the key one of Gammon when she was caught in the deep for 58.

It was fitting that Horley had the final say when she had Gemma Porter caught by Trussler.

Middlesex captain Saskia Horley said:

“It’s been a long day and I’m quite sore, but I think today proved how good this side is and how we stay together as a unit in quite challenging times.

“We gave ourselves a platform to express ourselves, then all our bowlers did their job and that’s what we’ve done all year.

“When we enjoy our cricket and we stick together as a group, these things can happen, a lot of girls have got jobs to go back to so enjoying it is phenomenal.

“That’s my final game for Middlesex which is bitter-sweet, but I’ll take in all of today and look back at these memories.

“There’s such a bright squad, we’ve got kids in here who are learning so much and that’s key in wanting to go professional.

“Glamorgan have got a phenomenal squad and I wish them good luck in Tier One, I think they’ll compete really well.”

Glamorgan vice-captain Bethan Gammon told BBC Sport Wales:

“It’s gutting to have ended up on the wrong side of it but fair play to Middlesex and their skipper who played a phenomenal innings to come out victorious.

“If we could go back and do the fielding innings again we would, we missed a few chances and they took full advantage.

“We tried to go out and be positive, Daisy Jeanes got off to a good start, Abbey and myself built up a pretty good partnership but the rate (needed) gradually grew over time.

“It was an incredibly proud season for us to see this team continue to grow and young players continue to shine, we’re continuing to develop a good team and a pathway to leave us in good stead for next year.”