Front brake discs replaced - but why are the brake lights on?

This is Dec built 2004 MGTF 135.
The brake discs have been replaced at the front with 280mm discs. Pads are new, hoses are new. One pipe had to be removed for inspection and refitted.
All back together and front callipers bled (based on pedal when turning the car around I’d say there is more air to dispel.
The filter basket is not yet back in the reservoir (as Im going to upgrade the rear).
When switching ignition on after reconnecting the battery the rear brake lights come on and appear to stay on.
Anyideas how to resolve this please?


 

Firstly it's good to see you replaced the discs etc. and made that brake pipe fit without leaking.
I'm not really sure what you mean about rear brake lights...it's not the handbrake light is it?
If it is the rear lights themselves then I reckon the brake light switch is stuck on.

One of the first job I had to do on my car, was replace the brake light switch........on inspection I found it to be cheap and nasty rubbish, I would check the switch hasn't just chosen this to be the ideal time to have a shit hemorrhage! 

https://www.the-t-bar.com/forum/9-mgf-tf-pitstop/89635-mgf-brake-pedal-resting-too-low

As TA22GT says, that's the most likely problem and easy to rectify.

That is useful information, thank you.
As I finished writing the initial post and moved on to more domestic chores I had a light bulb moment and thought it might be a switch and the pedal not returning enough.
That could be linked to air still in the system but heaven knows where. 
During the job of fitting new discs the old hoses were crimped off. Then when connecting up the new hose to the pipe there was very little loss at least hardly any on the off side. On the near side due to other circumstances the pipe had to be removed back to the ABS. With fluid seeping out of the fitting at the ABS a blank was fitted. So no air ingress there either. On re attaching the pipe fluid was allowed to drain through the calliper bleed nipple. On bleeding both sides steady fluid streams were observed i.e. no air other than the initial purge strokes of the pedal.
So why the pedal is near the floor and rather ineffective at present is a bit of a puzzle.

Best to give it a quick pressure bleed if you can. On my daily car i ended up with some air tracking back into the ABS unit though i was sure i had avoided it. Trying to bleed it normally just wasted time and brake fluid but pressure bleeding it removed it and restored normal pedal service very quickly. I assume its about giving the air bubble such a strong shove that it cant resist.

I seem to recall as the troublesome switch in my car was cheap and nasty plastic rubbish, I took it to a good old-fashioned  parts store that sill had proper knowledgeable staff behind the counter, not spotty 12 year olds who ask for rego numbers, And dropped it on the counter......Old mate had a quick look it and wandered out back for a good rummage about and wandered back to me holding a metal bodied one in his paw, he said it was for one the European designed Holden’s, basically badge engineered Opels of Poxhauls.
So the part was obviously fairly generic stuff that MG pillaged from someone else's parts bin, Ulike us here in Oz, given  your closer proximity to the natural habitat of Euro GM garbage, It should be easier for you Pomgolians to rummage up a better quality replacement if yours is plastic rubbish like mine was!
BTW.......I have no idea it the one my car had was OEM MG or some el cheapo generic shit, or indeed if the replacement one was OEM GM.
But replacing it with a more substantial one sorted the problem for me.

It is almost certainly air in the ABS pump causing a pedal to fall on the switch as others have pointed to.
Pressure bleeding it as per @Notanumber is the way forward.
Another way if the car is driveable, meaning it has some brake power, is to drive it slowly and try activate the ABS. That should allow the inner valves to force air in to the pipes and be released at a calliper.
I stay on a private road so that would be easy for me but perhaps not for everyone!
I am not sure of this but I believe some OBD readers allow you to operate the ecu on the ABS pump. P scan??

Before I start “digging around” in the vicinity of the switch on the pedal are there any others in the circuit such as a sensor in the ABS unit that might be sensing air in the ABS unit?
Obviously there is a significant loom connection at the ABS itself. 
And there is an odd looking connection in the “bonnet” area above each wing where the cable from the ABS sensors connect to the rest of the loom (one beneath the main fuse box for example). Are these connections unique in any way or just an IP67 connector?

If you look under the brake pedal you will see if it is resting on the switch. First port of call. I can't see anything else bringing the brake lights on.

As I recall there are two patterns of switch, one had a fixed plunger, with the second the plunger could be adjusted. When I first got the car I spent a lot of time with my arse in the air & head in the footwell trying to resolve a similar problem. Having worked out how to remove the switch it was replaced & services were resumed.
With the old one on the bench it became obvious that the plunger adjusts with one type to find the correct position, with the second type the switch body adjusts.
A comment on the quality. Cobber is only partly correct, had the materials been harder & the plunger diameter greater the device would have been fine. Having stripped it down the contacts were more than adequate for the job & showed no evidence of pitting.
M