The OED defines this sense of tosser:
1.b. [Probably < sense to toss off 4 at Phrasal verbs of the verb.]
A term of contempt or abuse for a person; a ‘jerk’. Cf. bugger n.1
3a.slang.
1977 Zigzag Apr. 40/3 She came on in a big mac and flashed her
legs like an old tosser before throwing it off.
1983 P. Inchbald Short Break in Venice xviii. 172 It's a right
pig's job... Poor little tosser. As if he wasn't suffering enough
already.
and:
jerk, n.1
5. slang (orig. U.S.). Someone of little or no account; a fool, a
stupid person. Cf. jerkwater n. b.
1935 A. J. Pollock Underworld Speaks 63/2 Jerk, a boob; chump; a
sucker.
1938 New Republic 7 Sept. 129/1 A jerk not only bores you but
pats you on the shoulder as he does so.
1945 Daily Express 11 Sept. 2/4 See this lighter? A dying Jerry
gave it to me. I gave the jerk a smoke from my last cigarette.
1950 E. Hemingway Across River xxxiii. 208 The brown-nosers..and
all the jerks.
1956 L. McIntosh Oxf. Folly 85 Julian sounds a dismal little
jerk when you sum him up like that.
1958 Listener 15 May 802/1 If..the sponsors get eight letters
saying that their comedian is an idiot, or a foul-mouthed jerk,
they're terrified.
At least 3 of those "jerk" quotations are from BrE sources.
This dictionary of "English slang and colloquialisms used in the United
Kingdom" says:
http://www.peevish.co.uk/slang/t.htm
tosser Noun. An idiot, a contemptible person. Also,
occasionally spelt tossa.
http://www.peevish.co.uk/slang/j.htm
jerk Noun. Idiot. [Orig U.S.]
--
Peter Duncanson, UK
(in alt.usage.english)