Sorry about the delay, all due to family distractions.
Well here's a list from one half of the Pesky Londoners,

and like you've said it's tough picking just Twelve, but here goes, and the other half should follow quite soon.
1. If Love Were All....from Alma Cogan, who gave so much in so short a time.
2. Over The Rainbow.... The Mormon Tabernacle Choir. my favourite version that holds a special memory.
3. Well Gather Lilacs, Sinatra doing perfect justice to this Ivor Novello song.
4. Strike Up The Band..., Matt Monro, showing that combined with the Great Nelson Riddle he could swing with the best.
5. Sanctuary Of The Heart....Albert Ketelby.. beautiful melody from British Light Music.
6. .Al Di La...... Al Martino.. meaning Beyond ( a 1961 Eurovision entry by Betty Curtis.--- but this is better.
7. It's Magic, ....Doris Day. -An early favourite for me and with servicemens regular requests on "Two-way Family Favourites."
8. I'll See You Again....Mario Lanza. Composer Noel Coward, and never sung better.
9. Let's Fall In Love.....Noel Coward --so clever, so funny.
10. Softly As I Leave You.... Matt Monro. perfect phrasing and meaningful lyrics.
11. Danny Boy....David Hughes Tenor, beautiful song, beautifully sung.
12. Fascination .....Al Martino... regarded as our song.

My First choice from this list I think would be "We'll Gather Lilacs" I adore Ivor Novello's music.
My memory goes back some years to a hotel in Jersey one evening when a pianist who was present had previously been pianist for Gracie Fields, Diana Dors and Vera Lynn.
He asked me what i would like him to play, and he played all Ivor Novello's classic numbers one after the other.
