I don't think it's a writ. It's part of a plea roll from the Court of Common Pleas, held at Westminster. This court heard civil disputes between individuals, often about debt, and the plea rolls briefly summarize the proceedings in each case.
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Joh(ann)es Olney Civis & Mercerus* london' in p(ro)pria p(er)sona sua op(tulit) se iiijto die v(er)sus Joh(ann)em Michell nup(er) de Dodford in
Com(itatu) Northt’ Gentilman de pl(ac)ito q(uo)d reddat ei viginti libras quas ei debet & iniuste detinet &c. Et ip(s)e non
ven(it) Et prec(eptum) fuit Vic(ecomitibus) q(uo)d cap(er)ent eum &c. Et Vic(ecomes) modo mand(at) q(uo)d non est invent(us) &c. I(de)o sicut prius capiat(ur)
q(uo)d sit hic a die Pasche in unu(m) mensem &c.
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John Olney, Citizen and Mercer* of London, presented himself on the fourth day in his own proper person, against John Michell, lately of Dodford in the county of Northants, gentleman, concerning a plea that he (Michell) should pay him twenty pounds which he owes him and is retaining unjustly etc. And he (Michell) did not come. And the sheriffs were instructed to arrest him etc. And the sheriff now states that he has not been found etc. Therefore, just as previously, he is to be arrested so that he is here within a month of Easter Day etc.
* capital M, I think, showing that he is of the Mercers’ Company of London (not just any old mercer).