Hairpin and simultaneous expressions

[David Sumbler]

\version "2.19.46"

\language "english"

%%Vn2 bars 276-279
\relative e' {
  \time 3/2 <e' c>1.\p\< ~ | q ~ | q | <c g> |
%%Vn2 bars 280-283
  << { \stemUp d2(\mp bf1 ~ | bf1. ~ | bf ~ | bf1)} \\ {f1. ~ | f ~ | f
~ | f1 } >> r2 |
}

The above extract from one of my files compiles to give the result I
want, except that it produces an "unterminated crescendo" warning; also
the p marking and the hairpin, which should start at bar 276 and end at
the mp marking in bar 280, do not appear.

I have tried moving the \mp to the lower note of the chord in bar 280,
which produces the same result, and I have also tried including it with
both upper and lower notes, which then gives 2 mp markings as well as
the warning.

What is the simplest way to achieve what I want?

David