install (node.js + npm required):

sudo npm install -g less

configure:

add less filter to assetic configuration:

# app/config/config.yml
# ...
# Assetic Configuration
assetic:
    debug:          %kernel.debug%
    use_controller: false
    filters:
        cssrewrite: ~
        less:
            node: /usr/bin/node
            node_paths: [/usr/lib/node_modules/]

using:

twig:

{% verbatim %}{% raw %}
{% stylesheets filter='less'
    '@QcmsAdminBundle/Resources/public/less/layout.less'
    '@QcmsAdminBundle/Resources/public/less/left-menu.less'
%}
    <link rel="stylesheet" href="{{ asset_url }}">
{% endstylesheets %}
{% endraw %}{% endverbatim %}