The European Union cannot afford to lose Turkey's interest in struggling accession talks, MPs have warned.
A report by the Commons' business and enterprise committee expresses concern that the process is in danger of stalling.
Disputes over Cyprus, the current constitutional crisis about the status of the ruling AK party and the slow pace of existing negotiations are all endangering the target date of 2014 for Turkey's accession to the EU, MPs say.
They are worried that Turkish perceptions of EU membership are being negatively affected by European leaders making clear their opposition to any such link-up.
Such signals, reducing the will to negotiate by Turkish leaders, would result in a "political disaster", they warn.
"Whatever its domestic challenges, Turkey has been pursuing reform," the report says.
"The EU can afford neither the political nor the economic consequences of a decision by Turkey, however reluctant, to turn its back on Europe."
Turkey's economy has progressed well since 2001 and it has made progress in changing its governance to fit with European norms.
MPs say these are facilitating businesses' work with the country but warn that this positive progress may be undone by open hostility to accession at this stage.
Committee chairman Peter Luff said: "The greatest danger we see is that Turkey may come to believe that the negotiations are not being conducted in good faith, and that accession will never be possible. We believe this would be a great loss to both sides."
The Foreign Office said it would not comment on the report in advance of its publication.