Like all sensible adults, I didn't tell the husband, daren't open the windows and hoped the problem would magically go away on it's own. Funnily enough, it didn't. Who would have thought...
A few weeks later, I finally admitted to myself that we would need to throw some money at this thing to make it go away. And devastatingly money which wouldn't make the house prettier, or add value, but rather keep the whole thing standing - to me that's the most annoying type of spending!
We had a few builders round to quote to retrofit a lintel above the window. We wanted to keep the actual frame as there was nothing wrong with it. Basically, the problem stems from when the houses were built and they were built with lovely structural timber window frames. Then in the 80's Mr Cheapskate who used to live here ripped them all out and replaced them with cheap PVC which is not structural. Essentially the window frames are therefore holding up the outer skin of bricks - not what they were designed to do.
A week later our chosen builder came round and fitted a lintel for the princely sum of £520. Admittedly we had a 2.4m window so it was a big bit of steel he put in there. Unfortunately I was at work that day, so I made the hubby take as many photos as he could without being a pest so I could see the process.
Overall it took the builder a day and a half to complete the job. You can see in the after photo (before he put some white sealant in the gap), how much the middle of the window frame had actually bent under the strain of the bricks. I think that's a permanent deformation now, but I'm glad we caught it when we did.