I'd like to hear some real medieval British music.
Oooh, I'm going to start with one, and go hunting for more.
King Richard I aka Richard the Lionheart wrote a piece of music while being held captive after the crusade, lamenting that he was being imprisoned, and how long it was taking for the ransom to be paid.
https://www.youtube.com/watch?v=DczZ_ZKbr_s
Text in original French:
I
Ja nus hons pris ne dira sa raison
Adroitement, se dolantement non;
Mais par effort puet il faire chançon.
Mout ai amis, mais povre sont li don;
Honte i avront se por ma reançon —
Sui ça deus yvers pris.
II
Ce sevent bien mi home et mi baron–
Ynglois, Normant, Poitevin et Gascon–
Que je n’ai nul si povre compaignon
Que je lessaisse por avoir en prison;
Je nou di mie por nule retraçon, —
Mais encor sui [je] pris.
III
Or sai je bien de voir certeinnement
Que morz ne pris n’a ami ne parent,
Quant on me faut por or ne por argent.
Mout m’est de moi, mes plus m’est de ma gent,
Qu’aprés ma mort avront reprochement —
Se longuement sui pris.
IV
N’est pas mervoille se j’ai le cuer dolant,
Quant mes sires met ma terre en torment.
S’il li membrast de nostre soirement
Quo nos feïsmes andui communement,
Je sai de voir que ja trop longuement —
Ne seroie ça pris.
V
Ce sevent bien Angevin et Torain–
Cil bacheler qui or sont riche et sain–
Qu’encombrez sui loing d’aus en autre main.
Forment m’amoient, mais or ne m’ainment grain.
De beles armes sont ore vuit li plain, —
Por ce que je sui pris
VI
Mes compaignons que j’amoie et que j’ain–
Ces de Cahen et ces de Percherain–
Di lor, chançon, qu’il ne sunt pas certain,
C’onques vers aus ne oi faus cuer ne vain;
S’il me guerroient, il feront que vilain —
Tant con je serai pris.
VII
Contesse suer, vostre pris soverain
Vos saut et gart cil a cui je m’en clain —
Et por cui je sui pris.
VIII
Je ne di mie a cele de Chartain, —
La mere Loës.
Now as part 2 of the answer, during a lot of the Middle Ages, the English monarchs were ostensibly French, and French was the language of the nobility for quite a while, mostly due to the Norman invasion of 1066. (I'll let the Medievalists chime in here, as I know some of this as it refers to music, but they'll know more about the alliances and changes of power that led to this)
A good example is Eleanor of Aquitaine, who was the mother of Richard I and John I, and the wife of Henry II (and earlier, Louis VII of France). She was a huge patron of the arts, and brought many musicians, and troubadours from France to entertain her. And during this time, many nobles were performing and even writing music - like the example of Richard I I already posted. These nobleman Troubadours became known as Trouvères (this name encompasses other musicians performing for nobility, as well as those that are noble born, but not the itinerant, poor minstrels of the time). They were writing and performing significant amounts of music, but were almost all French-born, and wrote in French. So a lot of the medieval British music would have been French. Certainly what survives anyway.
Some more well-known Touvères are:
Now these were often writing secular songs on the topic of love or nature, but there was also a great deal of religious music being written as well, unsurprisingly.
Some examples:
Now, outside of all this courtly music, there would be folk music written and performed by peasants, but this genre of music typically has few, if any, written records, and is often passed on by rote and played on simpler instruments. A good example is bagpipe music, which has survived despite all the bans and clearances by being passed down from person to person. However, finding recordings of what folk music would have sounded like a thousand years ago is going to be incredibly difficult.